feat: Add extra weight, price tracking, print history, usage analytics

- Extra Weight Field (#14): Track DryPods, custom holders in spool weight
  calculations. New extra_weight field on spool with DB migration.

- Price/Cost Tracking: Compute remaining_value based on remaining weight
  and price. Added column to spool list, inventory value on dashboard.

- Print History: Show print job history on spool detail page with
  collapsible table showing filename, filament used, status, dates.

- Usage Analytics: New dashboard component with time-series chart
  showing daily consumption, period selector (7/30/90 days), and
  material breakdown. New API endpoints for analytics data.

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

spoolman/database/models.py

@@ -100,6 +100,10 @@ class Spool(Base):
     initial_weight: Mapped[Optional[float]] = mapped_column()
     spool_weight: Mapped[Optional[float]] = mapped_column()
     used_weight: Mapped[float] = mapped_column()
+    extra_weight: Mapped[Optional[float]] = mapped_column(
+        default=None,
+        comment="Extra weight to account for (DryPods, custom holders, etc.).",
+    )
     location: Mapped[Optional[str]] = mapped_column(String(64), comment="Legacy flat location string.")
     location_id: Mapped[Optional[int]] = mapped_column(
         ForeignKey("location.id", ondelete="SET NULL"),