feat: Add quick wins batch (#42, #43, #25, #35, #20, #36, #39)

- #42: Allow spools heavier than theoretical max (remove weight clamps)
- #43: Show filament custom fields on spool detail page
- #25: Sort spools by custom fields and remaining weight
- #35: Global search box for spool list
- #20: Gallery view for spools (color grid with progress bars)
- #36: Spool-level color override with ColorPicker
- #39: Cost analytics endpoint, total spent & avg cost/kg stats
- Fix: Filament select refresh after inline creation
- Fix: Parse temperatures from filament comments

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

spoolman/api/v1/models.py

@@ -317,6 +317,12 @@ class Spool(BaseModel):
         description=("Extra weight to account for, such as DryPods, custom spool holders, etc."),
         examples=[50],
     )
+    color_hex: Optional[str] = Field(
+        default=None,
+        max_length=8,
+        description="Spool-level color override (hex code without #). Overrides the filament color if set.",
+        examples=["FF0000"],
+    )
     used_weight: float = Field(
         ge=0,
         description="Consumed weight of filament from the spool in grams.",
@@ -381,14 +387,14 @@ class Spool(BaseModel):
         remaining_length: Optional[float] = None
 
         if item.initial_weight is not None:
-            remaining_weight = max(item.initial_weight - item.used_weight, 0)
+            remaining_weight = item.initial_weight - item.used_weight
             remaining_length = length_from_weight(
                 weight=remaining_weight,
                 density=filament.density,
                 diameter=filament.diameter,
             )
         elif filament.weight is not None:
-            remaining_weight = max(filament.weight - item.used_weight, 0)
+            remaining_weight = filament.weight - item.used_weight
             remaining_length = length_from_weight(
                 weight=remaining_weight,
                 density=filament.density,