feat: dual external spool support, AMS slot model filtering & pre-population

Backend:
- Add dual external spool support for H2D (vt_tray as list: Ext-L/Ext-R)
- Add cloud filament ID map endpoint (/cloud/filament-id-map)
- Fix RFID spool data erased by periodic AMS updates (skip tag matcher
  for RFID-tagged trays)
- Fix AMS slot config overwrites RFID spool state
- Fix K-profile selection corrupts existing profiles on X1C/P1S
- Resolve K-profiles filament name via cloud filament ID map
- Update print scheduler and usage tracker for dual external spools

Frontend:
- Add printer model filtering to ConfigureAmsSlotModal (cloud/local/builtin
  presets filtered by @BBL model suffix and compatible_printers)
- Add pre-population for configured slots (preset, color, K-profile)
- Add K-Profiles view with accurate filament name resolution
- Internationalize all ConfigureAmsSlotModal strings (en/de/fr/it/ja — 21 keys)
- Add 5 new ConfigureAmsSlotModal tests (model filtering, pre-selection,
  color pre-population, i18n)
- Update PrintersPage for dual external spool rendering

Docs:
- Update CHANGELOG, README, website features, and wiki AMS docs

frontend/src/components/AssignSpoolModal.tsx

@@ -62,15 +62,17 @@ export function AssignSpoolModal({ isOpen, onClose, printerId, amsId, trayId, tr
 
   if (!isOpen) return null;
 
-  // Filter out Bambu Lab spools (identified by RFID tag_uid or tray_uuid)
-  // and spools already assigned to other slots
+  // Filter out spools already assigned to other slots
   const assignedSpoolIds = new Set(
     (assignments || [])
       .filter(a => !(a.printer_id === printerId && a.ams_id === amsId && a.tray_id === trayId))
       .map(a => a.spool_id)
   );
+  // External slots (amsId 254 or 255) have no RFID reader, so show all spools.
+  // AMS slots only show manual spools (no tag_uid or tray_uuid).
+  const isExternalSlot = amsId === 254 || amsId === 255;
   const manualSpools = spools?.filter((spool: InventorySpool) =>
-    !spool.tag_uid && !spool.tray_uuid && !assignedSpoolIds.has(spool.id)
+    !assignedSpoolIds.has(spool.id) && (isExternalSlot || (!spool.tag_uid && !spool.tray_uuid))
   );
 
   const filteredSpools = manualSpools?.filter((spool: InventorySpool) => {