Add multi-plate 3MF plate selection for reprinting (Issue #93)

When reprinting a multi-plate 3MF file exported with "All sliced file",
the system now asks which plate to print and only maps filaments for
that specific plate.

Backend changes:
- Add GET /archives/{id}/plates endpoint to list available plates
  with thumbnails, print times, and per-plate filament requirements
- Add GET /archives/{id}/plate-thumbnail/{index} for plate thumbnails
- Update GET /archives/{id}/filament-requirements to accept plate_id
  query parameter for filtering filaments by plate
- Add plate_id field to ReprintRequest schema
- Update POST /archives/{id}/reprint to use plate_id from request body
  instead of auto-detecting (maintains backward compatibility)

Frontend changes:
- Add getArchivePlates API method
- Update getArchiveFilamentRequirements to accept optional plateId
- Update reprintArchive to accept plate_id in options
- Add plate selection UI to ReprintModal when multi-plate 3MF detected
- Show plate thumbnails, names, and filament counts in selection grid
- Require plate selection before printing multi-plate files
- Filter filament requirements to show only selected plate's filaments

Tests:
- Add unit tests for multi-plate slice_info.config parsing
- Add unit tests for plate detection from gcode files
- Add integration tests for new plate endpoints

static/index.html

@@ -23,7 +23,7 @@
 
     <!-- Splash screens for iOS -->
     <link rel="apple-touch-startup-image" href="/img/android-chrome-512x512.png" />
-    <script type="module" crossorigin src="/assets/index-CVMDsKi7.js"></script>
+    <script type="module" crossorigin src="/assets/index-BNfnoADT.js"></script>
     <link rel="stylesheet" crossorigin href="/assets/index-Dzh7xD3q.css">
   </head>
   <body>