feat: Add temperature ranges for extruder and bed temps (#5)

Store extruder and bed temperatures as min/max ranges instead of
single values for more accurate filament specifications.

Backend changes:
- Add 4 new columns: settings_extruder_temp_min/max, settings_bed_temp_min/max
- Keep old columns for backward compatibility (marked deprecated)
- Alembic migration copies existing values to both min and max
- Update Pydantic models and API endpoints

Frontend changes:
- Filament model updated with new fields
- Create form uses min/max input pairs with Space.Compact
- Import from external DB populates both min and max with same value
- Label template updated to show ranges: "ET: 190-220 °C"
- Template help includes new tags

Labels now display temperature ranges like "190-220°C" which is more
useful for printing than a single recommended value.

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

spoolman/database/filament.py

@@ -41,6 +41,10 @@ async def create(
     comment: Optional[str] = None,
     settings_extruder_temp: Optional[int] = None,
     settings_bed_temp: Optional[int] = None,
+    settings_extruder_temp_min: Optional[int] = None,
+    settings_extruder_temp_max: Optional[int] = None,
+    settings_bed_temp_min: Optional[int] = None,
+    settings_bed_temp_max: Optional[int] = None,
     color_hex: Optional[str] = None,
     multi_color_hexes: Optional[str] = None,
     multi_color_direction: Optional[MultiColorDirection] = None,
@@ -69,6 +73,10 @@ async def create(
         comment=comment,
         settings_extruder_temp=settings_extruder_temp,
         settings_bed_temp=settings_bed_temp,
+        settings_extruder_temp_min=settings_extruder_temp_min,
+        settings_extruder_temp_max=settings_extruder_temp_max,
+        settings_bed_temp_min=settings_bed_temp_min,
+        settings_bed_temp_max=settings_bed_temp_max,
         color_hex=color_hex,
         multi_color_hexes=multi_color_hexes,
         multi_color_direction=multi_color_direction.value if multi_color_direction is not None else None,