feat(printer): support Filament Track Switch (FTS) accessory in print modal (#1162)

The FTS routes any AMS slot to either extruder, so AMS info reports
  bits 8-11 = 0xE (uninitialized) and ams_extruder_map ends up empty.
  The print modal's per-nozzle dropdown filter then hides every loaded
  slot, leaving the user with an empty filament dropdown.

  Detection: parse print.device.fila_switch from MQTT push_status into a
  new FilaSwitchState dataclass on PrinterState; surface it through the
  GET /printers/{id}/status response as a nullable FilaSwitchResponse.

  Frontend: useFilamentMapping and FilamentMapping skip the per-extruder
  filter when fila_switch.installed is true. Slots currently fed into a
  track display an [L]/[R] routing badge in the dropdown so the user
  can see where the FTS is currently routing them.

  Tests: 4 backend unit (TestFilamentTrackSwitchDetection), 2 backend
  integration (status route), 2 hook regression, 2 component regression.

frontend/src/hooks/useFilamentMapping.ts

@@ -96,6 +96,10 @@ export function computeAmsMapping(
   const loadedFilaments = buildLoadedFilaments(printerStatus);
   if (loadedFilaments.length === 0) return undefined;
 
+  // FTS routes any AMS slot to any extruder, so per-nozzle slot restriction
+  // doesn't apply when it's installed (#1162).
+  const ftsActive = printerStatus?.fila_switch?.installed === true;
+
   // Track which trays have been assigned to avoid duplicates
   const usedTrayIds = new Set<number>();
 
@@ -108,7 +112,8 @@ export function computeAmsMapping(
     // Nozzle-aware filtering: restrict to trays on the correct nozzle.
     // This is a hard filter — cross-nozzle assignment causes print failures
     // ("position of left hotend is abnormal"), so we never fall back to wrong-nozzle trays.
-    if (req.nozzle_id != null) {
+    // Skip when an FTS is installed: it can route any slot to either extruder.
+    if (req.nozzle_id != null && !ftsActive) {
       available = available.filter((f) => f.extruderId === req.nozzle_id);
     }
 
@@ -311,6 +316,10 @@ export function useFilamentMapping(
 ): UseFilamentMappingResult {
   const loadedFilaments = useLoadedFilaments(printerStatus);
 
+  // FTS routes any AMS slot to any extruder, so per-nozzle slot restriction
+  // doesn't apply when it's installed (#1162).
+  const ftsActive = printerStatus?.fila_switch?.installed === true;
+
   const filamentComparison = useMemo(() => {
     if (!filamentReqs?.filaments || filamentReqs.filaments.length === 0) return [];
 
@@ -363,7 +372,8 @@ export function useFilamentMapping(
 
       // Nozzle-aware filtering: restrict to trays on the correct nozzle.
       // This is a hard filter — cross-nozzle assignment causes print failures.
-      if (req.nozzle_id != null) {
+      // Skip when an FTS is installed: it can route any slot to either extruder.
+      if (req.nozzle_id != null && !ftsActive) {
         available = available.filter((f) => f.extruderId === req.nozzle_id);
       }
 
@@ -469,7 +479,7 @@ export function useFilamentMapping(
         isManual: false,
       };
     });
-  }, [filamentReqs, loadedFilaments, manualMappings, preferLowest]);
+  }, [filamentReqs, loadedFilaments, manualMappings, preferLowest, ftsActive]);
 
   // Build AMS mapping from matched filaments
   // Format: array matching 3MF filament slot structure