feat: Add spool adjustment history tracking (#6)

Track history of all spool weight/length adjustments with timestamps and comments:

Backend:
- Add SpoolAdjustment database model with spool_id, timestamp, type, value, comment
- Add Alembic migration for spool_adjustment table
- Add SpoolAdjustment Pydantic model for API responses
- Update use_weight, use_length, and measure functions to record adjustments
- Add GET /api/v1/spool/{id}/adjustments endpoint for history retrieval
- Add optional comment parameter to use/measure endpoints

Frontend:
- Add ISpoolAdjustment interface to spool model
- Add collapsible adjustment history table to spool show page
- Display timestamp, type (weight/length), amount, and comment
- Add translation keys for history table

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

spoolman/api/v1/models.py

@@ -388,6 +388,29 @@ class Spool(BaseModel):
         )
 
 
+class SpoolAdjustment(BaseModel):
+    """Record of a spool weight/length adjustment."""
+
+    id: int = Field(description="Unique internal ID of this adjustment.")
+    spool_id: int = Field(description="The spool this adjustment belongs to.")
+    timestamp: SpoolmanDateTime = Field(description="When the adjustment was made. UTC Timezone.")
+    adjustment_type: str = Field(description="Type of adjustment: 'weight' or 'length'.")
+    value: float = Field(description="Amount adjusted (negative = used, positive = added).")
+    comment: Optional[str] = Field(None, description="Optional user comment about this adjustment.")
+
+    @staticmethod
+    def from_db(item: models.SpoolAdjustment) -> "SpoolAdjustment":
+        """Create a new Pydantic SpoolAdjustment object from a database object."""
+        return SpoolAdjustment(
+            id=item.id,
+            spool_id=item.spool_id,
+            timestamp=item.timestamp,
+            adjustment_type=item.adjustment_type,
+            value=item.value,
+            comment=item.comment,
+        )
+
+
 class Info(BaseModel):
     version: str = Field(examples=["0.7.0"])
     debug_mode: bool = Field(examples=[False])