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>

alembic/versions/0008_job_material_color.py

@@ -0,0 +1,26 @@
+"""add job_material and job_color to print_jobs
+
+Revision ID: 0008
+Revises: 0007
+Create Date: 2026-06-18
+
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0008"
+down_revision: Union[str, None] = "0007"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column("print_jobs", sa.Column("job_material", sa.String(50), nullable=True))
+    op.add_column("print_jobs", sa.Column("job_color", sa.String(100), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("print_jobs", "job_color")
+    op.drop_column("print_jobs", "job_material")