Refactor Spoolman per-filament tracking (PR #277 follow-up)

Extract Spoolman tracking from main.py into dedicated service module,
DRY up repeated helpers, add i18n for new settings UI, and add tests.

- Move ~460 lines from main.py to services/spoolman_tracking.py
- Extract _resolve_spool_tag, _resolve_global_tray_id, build_ams_tray_lookup helpers
- Replace fragile tuple return in get_spoolman_settings() with dict
- Wire 4 new UI strings through i18n (en/de/ja)
- Add 42 backend unit tests (spoolman tracking helpers + 3MF parsing)
- Add 6 frontend tests for weight sync and partial usage toggles
- Update CHANGELOG, wiki, and website docs

Closes PR #277

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-DJ147FSl.js"></script>
+    <script type="module" crossorigin src="/assets/index-AXQRHtw2.js"></script>
     <link rel="stylesheet" crossorigin href="/assets/index-togsBDt6.css">
   </head>
   <body>