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>

migrations/versions/2025_01_15_0200-a1b2c3d4e5f6_add_temperature_ranges.py

@@ -0,0 +1,56 @@
+"""add_temperature_ranges.
+
+Revision ID: a1b2c3d4e5f6
+Revises: 415a8f855e14
+Create Date: 2025-01-15 02:00:00.000000
+"""
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "a1b2c3d4e5f6"
+down_revision = "415a8f855e14"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    """Add temperature range columns and migrate existing data."""
+    # Add new columns for temperature ranges
+    op.add_column("filament", sa.Column("settings_extruder_temp_min", sa.Integer(), nullable=True))
+    op.add_column("filament", sa.Column("settings_extruder_temp_max", sa.Integer(), nullable=True))
+    op.add_column("filament", sa.Column("settings_bed_temp_min", sa.Integer(), nullable=True))
+    op.add_column("filament", sa.Column("settings_bed_temp_max", sa.Integer(), nullable=True))
+
+    # Migrate existing single temp values to both min and max
+    # This preserves the existing data while enabling the new range functionality
+    connection = op.get_bind()
+    connection.execute(
+        sa.text(
+            """
+            UPDATE filament
+            SET settings_extruder_temp_min = settings_extruder_temp,
+                settings_extruder_temp_max = settings_extruder_temp
+            WHERE settings_extruder_temp IS NOT NULL
+            """
+        )
+    )
+    connection.execute(
+        sa.text(
+            """
+            UPDATE filament
+            SET settings_bed_temp_min = settings_bed_temp,
+                settings_bed_temp_max = settings_bed_temp
+            WHERE settings_bed_temp IS NOT NULL
+            """
+        )
+    )
+
+
+def downgrade() -> None:
+    """Remove temperature range columns."""
+    op.drop_column("filament", "settings_bed_temp_max")
+    op.drop_column("filament", "settings_bed_temp_min")
+    op.drop_column("filament", "settings_extruder_temp_max")
+    op.drop_column("filament", "settings_extruder_temp_min")