feat: color picker, unified UI styling, filament mismatch detection, Spoolman slot assignment

- Slot color editor: Pickr HSV color picker (offline, served from lib/),
  recent swatches (up to 16, localStorage), copy color from other slot
- Unified axes control panel: XY+Z merged, shared step size + custom mm input
- Language selector moved from header to Settings → Appearance
- Filament mismatch detection blocks Upload-and-Print on material mismatch,
  slot mapper opens automatically
- Spoolman spool-per-slot assignment in AMS status tab and Filaments settings
- Fix: Spoolman sync rate label — 0=end of print, not disabled (Issue #76)
- Fix: lib/ assets served by bridge static handler for offline use
- UI: global unified select + input styling, set-row labels match modal-field

web/translations/en.json

@@ -123,7 +123,7 @@
   "lbl_light": "💡 Light",
   "lbl_remaining": "Remaining:",
   "lbl_slicer_time": "Slicer estimate:",
-  "lbl_spoolman_sync_rate": "Sync rate (s, 0=off)",
+  "lbl_spoolman_sync_rate": "Sync rate (s, 0=end of print)",
   "lbl_spoolman_url": "Server URL",
   "lbl_unload": "Unload",
   "lbl_zpos": "Z (mm)",
@@ -324,5 +324,6 @@
   "update_docker_copied": "Copied! Run: docker compose pull && docker compose up -d",
   "update_error": "Error",
   "update_none": "Already up to date",
-  "update_restarting": "Restarting..."
+  "update_restarting": "Restarting...",
+  "slot_copy_from": "Copy color from slot…"
 }