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/spool.py

@@ -212,6 +212,17 @@ async def find(
             ),
         ),
     ] = None,
+    filament_color_hex: Annotated[
+        Optional[str],
+        Query(
+            alias="filament.color_hex",
+            title="Filament Color",
+            description=(
+                "Filter by exact filament color hex code (without #). Separate multiple colors with a comma."
+            ),
+            examples=["FF0000", "FF0000,00FF00,0000FF"],
+        ),
+    ] = None,
     filament_vendor_name: Annotated[
         Optional[str],
         Query(
@@ -321,6 +332,7 @@ async def find(
         filament_name=filament_name if filament_name is not None else filament_name_old,
         filament_id=filament_ids,
         filament_material=filament_material if filament_material is not None else filament_material_old,
+        filament_color_hex=filament_color_hex,
         vendor_name=filament_vendor_name if filament_vendor_name is not None else vendor_name_old,
         vendor_id=filament_vendor_ids,
         location=location,