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/models.py

@@ -46,8 +46,12 @@ class Filament(Base):
     spool_weight: Mapped[Optional[float]] = mapped_column(comment="The weight of an empty spool.")
     article_number: Mapped[Optional[str]] = mapped_column(String(64))
     comment: Mapped[Optional[str]] = mapped_column(String(1024))
-    settings_extruder_temp: Mapped[Optional[int]] = mapped_column(comment="Overridden extruder temperature.")
-    settings_bed_temp: Mapped[Optional[int]] = mapped_column(comment="Overridden bed temperature.")
+    settings_extruder_temp: Mapped[Optional[int]] = mapped_column(comment="Overridden extruder temperature (deprecated, use min/max).")
+    settings_bed_temp: Mapped[Optional[int]] = mapped_column(comment="Overridden bed temperature (deprecated, use min/max).")
+    settings_extruder_temp_min: Mapped[Optional[int]] = mapped_column(comment="Minimum extruder temperature.")
+    settings_extruder_temp_max: Mapped[Optional[int]] = mapped_column(comment="Maximum extruder temperature.")
+    settings_bed_temp_min: Mapped[Optional[int]] = mapped_column(comment="Minimum bed temperature.")
+    settings_bed_temp_max: Mapped[Optional[int]] = mapped_column(comment="Maximum bed temperature.")
     color_hex: Mapped[Optional[str]] = mapped_column(String(8))
     multi_color_hexes: Mapped[Optional[str]] = mapped_column(String(128))
     multi_color_direction: Mapped[Optional[str]] = mapped_column(String(16))