Replace combined filament dropdown with separate material + color dropdowns

- app/constants.py: MATERIALS and COLORS standard value lists
- Migration 0008: job_material + job_color columns on print_jobs
- Job creation (both /jobs and /brackets/{id}/jobs) stores these independently
  of the filament inventory
- All job tables updated to display job_material · job_color

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/models/print_job.py

@@ -28,6 +28,8 @@ class PrintJob(Base):
     name: Mapped[str] = mapped_column(String(200))
     customer: Mapped[str | None] = mapped_column(String(200))
     file_name: Mapped[str | None] = mapped_column(String(255))
+    job_material: Mapped[str | None] = mapped_column(String(50))
+    job_color: Mapped[str | None] = mapped_column(String(100))
     status: Mapped[JobStatus] = mapped_column(Enum(JobStatus), default=JobStatus.queued)
     queue_position: Mapped[int | None] = mapped_column(Integer)
     started_at: Mapped[datetime | None] = mapped_column(DateTime)