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/database/models.py

@@ -85,6 +85,25 @@ class Spool(Base):
         cascade="save-update, merge, delete, delete-orphan",
         lazy="joined",
     )
+    adjustments: Mapped[list["SpoolAdjustment"]] = relationship(
+        back_populates="spool",
+        cascade="save-update, merge, delete, delete-orphan",
+        lazy="noload",  # Don't load by default, only on explicit request
+    )
+
+
+class SpoolAdjustment(Base):
+    """Track history of spool weight/length adjustments."""
+
+    __tablename__ = "spool_adjustment"
+
+    id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    spool_id: Mapped[int] = mapped_column(ForeignKey("spool.id", ondelete="CASCADE"), index=True)
+    spool: Mapped["Spool"] = relationship(back_populates="adjustments")
+    timestamp: Mapped[datetime] = mapped_column(comment="When the adjustment was made.")
+    adjustment_type: Mapped[str] = mapped_column(String(16), comment="Type: 'weight' or 'length'.")
+    value: Mapped[float] = mapped_column(comment="Amount adjusted (negative = used, positive = added).")
+    comment: Mapped[Optional[str]] = mapped_column(String(256), comment="Optional user comment.")
 
 
 class Setting(Base):