Analyse STL/3MF on upload: bounding box + volume, cached in stl_cache

- StlCache model: filename, cube_x/y/z (mm), volume_ccm
- Migration 0007: stl_cache table
- app/stl_analysis.py: trimesh-based analyse() + get_cache_map()
  - Runs immediately after upload in both /jobs and /brackets/{id}/jobs
  - Skips .gcode (no geometry), caches per filename, idempotent
- Library selector in both modals now shows dimensions and volume
- requirements: trimesh==4.5.3

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

alembic/versions/0007_stl_cache.py

@@ -0,0 +1,35 @@
+"""stl_cache table for bounding box and volume
+
+Revision ID: 0007
+Revises: 0006
+Create Date: 2026-06-18
+
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0007"
+down_revision: Union[str, None] = "0006"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "stl_cache",
+        sa.Column("id", sa.Integer(), autoincrement=True, nullable=False),
+        sa.Column("filename", sa.String(255), nullable=False),
+        sa.Column("cube_x", sa.Float(), nullable=True),
+        sa.Column("cube_y", sa.Float(), nullable=True),
+        sa.Column("cube_z", sa.Float(), nullable=True),
+        sa.Column("volume_ccm", sa.Float(), nullable=True),
+        sa.Column("created_at", sa.DateTime(), nullable=False, server_default=sa.text("CURRENT_TIMESTAMP")),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint("filename"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("stl_cache")