Show Spoolman fill level for AMS Lite and external spools (#293)

AMS Lite units (A1 series) have no weight sensor and always report 0%
fill level. When a spool is linked to Spoolman with weight data, use
Spoolman's remaining weight as a fallback. External spools also show
fill level from Spoolman data instead of always showing unknown.

Backend: Enrich GET /spoolman/spools/linked response with
remaining_weight and filament_weight alongside spool ID.

Frontend: Add getSpoolmanFillLevel() helper. Update regular AMS, HT
AMS, and external spool fill computations to use Spoolman fallback
when AMS reports 0%. Show "(Spoolman)" indicator in hover card when
fill data comes from Spoolman.

backend/app/api/routes/spoolman.py

@@ -598,7 +598,7 @@ async def get_linked_spools(
         raise HTTPException(status_code=503, detail="Spoolman is not reachable")
 
     spools = await client.get_spools()
-    linked: dict[str, int] = {}
+    linked: dict[str, dict] = {}
 
     for spool in spools:
         # Check if spool has a tag in extra field
@@ -608,7 +608,12 @@ async def get_linked_spools(
             # Remove quotes if present (JSON encoded string)
             clean_tag = tag.strip('"').upper()
             if clean_tag:
-                linked[clean_tag] = spool["id"]
+                filament = spool.get("filament") or {}
+                linked[clean_tag] = {
+                    "id": spool["id"],
+                    "remaining_weight": spool.get("remaining_weight"),
+                    "filament_weight": filament.get("weight"),
+                }
 
     return {"linked": linked}