● feat(slicer): server-side slicing via OrcaSlicer / Bambu Studio sidecar

Adds an optional slicer-api/ Compose stack and wires Bambuddy's File
  Manager, Archives, and MakerWorld pages to a new server-side Slice flow.
  Slicing runs as an in-memory background job (POST returns 202 + job_id,
  polled via GET /api/v1/slice-jobs/{id}) so a multi-minute slice no
  longer pins the modal; result lands as a new .gcode.3mf in the same
  folder (or new archive for archive sources) with the embedded
  thumbnail extracted.

  Backend
  - New services: slice_dispatch (in-memory dispatcher, 30min retention
    sweep) and slicer_api (HTTP bridge with 4xx/5xx/connection error
    split that drives the 3MF embedded-settings fallback retry path).
  - New schemas: SliceRequest, SliceResponse, SliceArchiveResponse,
    SliceJobEnqueueResponse.
  - New routes: POST /library/files/{id}/slice,
    POST /archives/{id}/slice, GET /api/v1/slice-jobs/{id} (gated on
    LIBRARY_READ since job IDs are sequential and the body leaks source
    filenames and result IDs).
  - AppSettings + env defaults: use_slicer_api, orcaslicer_api_url,
    bambu_studio_api_url. DB-stored values override env defaults.

  Frontend
  - New SliceModal handles preset gating; enqueues then closes
    immediately.
  - New SliceJobTrackerProvider polls active jobs at app level, surfaces
    a single toast per job (queued -> running -> completed / failed)
    and invalidates library/archives queries on terminal status.
  - Settings -> Workflow -> Slicer card: preferred slicer dropdown,
    Use Slicer API toggle, contextual sidecar URL field.
  - File Manager / Archives / MakerWorld get a Slice button gated on
    the Use Slicer API setting.
  - gcode-viewer adapter learns ?library_file=<id> so sliced library
    files preview inline.

  i18n
  - New slice.* and settings.{useSlicerApi,slicerCard,orcaslicerApiUrl,
    bambuStudioApiUrl,slicerApiUrlDescription,useSlicerApiDescription}
    + fileManager.noPermissionSlice keys across all 8 locales (en, de,
    fr, it, ja, pt-BR, zh-CN, zh-TW). English fully translated, German
    fully translated, the other six seeded with English fallbacks
    pending native translation.

  Tests
  - 10 backend integration tests in test_library_slice_api.py covering
    validation (404/400), happy-path enqueue, sidecar-down, 3MF
    embedded-settings fallback, STL no-fallback, and preset-error ->
    failed job paths.
  - New unit tests in test_slicer_api.py for the HTTP bridge.
  - 5 new SliceModal frontend tests covering preset gating, library +
    archive enqueue paths, error surface, and preset-load failure.
  - Existing SettingsPage tests adjusted: slicer dropdown asserts now
    switch to the Workflow tab first; added a beforeEach URL reset so
    one test's tab click doesn't bleed into sibling tests.

  Sidecar
  - New slicer-api/ folder is self-contained and optional. Two services
    (orca-slicer-api on 3003, bambu-studio-api on 3001 behind --profile
    bambu) build via Docker git-build-context from
    maziggy/orca-slicer-api@bambuddy/profile-resolver. The fork patches
    the OrcaSlicer CLI's profile compatibility quirks (inherits-chain
    resolver, from:User -> system rewrite, '# ' clone-prefix strip,
    sentinel-value strip) empirically required to slice real GUI
    exports without segfaulting the CLI.

  Docs
  - CHANGELOG entry under [0.2.4b1] - Unreleased Added.
  - README File Manager bullet for the new server-side Slice button.
  - bambuddy-website features.html: new card under "Configurable Slicer".
  - bambuddy-wiki: new page features/slicer-api.md + nav entry +
    features index card.

  Notes
  - Opt-in: with Use Slicer API off, the existing "open in desktop
    slicer via URI" flow is the default and unchanged.
  - 3MF inputs that segfault the CLI on --load-settings transparently
    retry with embedded settings; the resulting job carries
    used_embedded_settings: true.
  - Sliced files always export as .gcode.3mf so File Manager picks up
    the embedded thumbnail; file_type is set to "gcode" (blue badge).

gcode_viewer/js/bambuddy_adapter.js

@@ -180,6 +180,13 @@
                 /^\/?downloads\/files\/local\/__bambuddy_archive_(\d+)$/,
                 API_BASE + '/archives/$1/gcode'
             );
+            // OctoPrint file download  →  Bambuddy library file gcode
+            // (sliced LibraryFile — extracts embedded gcode from .gcode.3mf
+            // or returns plain .gcode). Plate is ignored upstream for now.
+            newPath = newPath.replace(
+                /^\/?downloads\/files\/local\/__bambuddy_libgcode_(\d+)(?:_plate\d+)?$/,
+                API_BASE + '/library/files/$1/gcode'
+            );
             // OctoPrint plugin static assets  →  gcode-viewer static files
             newPath = newPath.replace(
                 /^\/?plugin\/prettygcode\/static\//,
@@ -411,6 +418,57 @@
             .catch(function () { /* best-effort — default bed stays */ });
     }
 
+    // -------------------------------------------------------------------------
+    // 10b. Library file loader — invoked via /gcode-viewer/?library_file=<id>
+    // -------------------------------------------------------------------------
+    function loadLibraryFileById(fileId, plate) {
+        // Mirror loadArchiveById, but use the library gcode endpoint. The
+        // /library/files/<id>/gcode endpoint extracts the embedded gcode
+        // from a .gcode.3mf or returns a plain .gcode body. It does not
+        // accept a plate selector today — multi-plate library files would
+        // need an upstream change. The plate suffix here is preserved in
+        // currentFilename for display only.
+        var plateSuffix = (typeof plate === 'number' && plate >= 1) ? ('_plate' + plate) : '';
+        currentFileId = 'libfile_' + fileId + plateSuffix;
+        currentFilename = 'Library file #' + fileId + (plateSuffix ? (' (plate ' + plate + ')') : '');
+        currentFileDate = Date.now();
+        gcodeLayerMap = null;
+        lastFedLayer = -1;
+        stopPlayback(true);
+        updateFilenameDisplay(currentFilename);
+        var playBtn = document.getElementById('bb-play-btn');
+        if (playBtn) playBtn.disabled = false;
+        if (viewModel && viewModel.fromCurrentData) {
+            viewModel.fromCurrentData({
+                job: {
+                    file: {
+                        path: '__bambuddy_libgcode_' + fileId + plateSuffix,
+                        date: currentFileDate,
+                    },
+                    estimatedPrintTime: null,
+                },
+                state: { text: 'Operational', flags: { printing: false } },
+                progress: { filepos: null, completion: 0 },
+                currentZ: null,
+                logs: [],
+            });
+        }
+
+        // Fetch metadata for the filename display. There is no
+        // /library/files/<id>/capabilities endpoint, so the bed stays at
+        // whatever the default fakePrinterProfile is set to.
+        apiFetch('/library/files/' + fileId, {})
+            .then(function (r) { return r.ok ? r.json() : null; })
+            .then(function (meta) {
+                if (meta && (meta.print_name || meta.filename)) {
+                    currentFilename = (meta.print_name || meta.filename) +
+                        (plateSuffix ? (' (plate ' + plate + ')') : '');
+                    updateFilenameDisplay(currentFilename);
+                }
+            })
+            .catch(function () { /* best-effort — filename stays "Library file #N" */ });
+    }
+
     // -------------------------------------------------------------------------
     // 11. Initialise after DOM + scripts are ready
     // -------------------------------------------------------------------------
@@ -548,19 +606,23 @@
     function onDomReady() {
         setTimeout(function () {
             init();
-            // If the viewer was opened with ?archive=<id>[&plate=<N>], load that
-            // archive's gcode for the requested plate once the viewmodel is ready.
+            // If the viewer was opened with ?archive=<id>[&plate=<N>] or
+            // ?library_file=<id>[&plate=<N>], load that source's gcode once
+            // the viewmodel is ready.
             try {
                 var params = new URLSearchParams(window.location.search);
                 var archiveParam = params.get('archive');
+                var libParam = params.get('library_file');
                 var plateParam = params.get('plate');
+                var plateId = (plateParam && /^[1-9][0-9]*$/.test(plateParam))
+                    ? parseInt(plateParam, 10)
+                    : undefined;
                 if (archiveParam && /^[1-9][0-9]*$/.test(archiveParam)) {
                     var archiveId = parseInt(archiveParam, 10);
-                    var plateId = (plateParam && /^[1-9][0-9]*$/.test(plateParam))
-                        ? parseInt(plateParam, 10)
-                        : undefined;
-                    // Allow a tick for init() to finish wiring viewModel.fromCurrentData
                     setTimeout(function () { loadArchiveById(archiveId, plateId); }, 50);
+                } else if (libParam && /^[1-9][0-9]*$/.test(libParam)) {
+                    var libId = parseInt(libParam, 10);
+                    setTimeout(function () { loadLibraryFileById(libId, plateId); }, 50);
                 }
             } catch (e) { /* URLSearchParams unsupported — skip */ }
         }, 200);
@@ -577,6 +639,7 @@
     // -------------------------------------------------------------------------
     window.BambuddyPrettyGCode = {
         loadArchive: loadArchiveById,
+        loadLibraryFile: loadLibraryFileById,
         getViewModel: function () { return viewModel; },
         play: startPlayback,
         stop: stopPlayback,