feat: Add color column with filter to spool list

Add optional color column to spool list showing filament color swatches
with multi-select filtering capability.

Backend:
- GET /api/v1/color endpoint to list distinct filament colors
- filament.color_hex query param on spool list for filtering

Frontend:
- ColorFilterColumn component renders color swatches
- useSpoolmanColors() hook fetches available colors
- Filter dropdown shows swatches with hex codes
- Column hidden by default (enable via column selector)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

spoolman/api/v1/other.py

@@ -47,6 +47,33 @@ async def find_materials(
     return await filament.find_materials(db=db)
 
 
+@router.get(
+    "/color",
+    name="Find colors",
+    description="Get a list of all filament colors (hex codes).",
+    response_model_exclude_none=True,
+    responses={
+        200: {
+            "description": "A list of all filament color hex codes.",
+            "content": {
+                "application/json": {
+                    "example": [
+                        "FF0000",
+                        "00FF00",
+                        "0000FF",
+                    ],
+                },
+            },
+        },
+    },
+)
+async def find_colors(
+    *,
+    db: Annotated[AsyncSession, Depends(get_db_session)],
+) -> list[str]:
+    return await filament.find_colors(db=db)
+
+
 @router.get(
     "/article-number",
     name="Find article numbers",