feat: rich product metadata extraction from STEP files

Extract volume, surface area, part count, assembly hierarchy, and
complexity from STEP files via OCC B-rep analysis.

Backend:
- extract_rich_metadata() in step_processor.py: computes per-part volume
  (BRepGProp), surface area, triangle/vertex count, assembly depth,
  instance count, complexity score, largest part identification
- cad_metadata JSONB column on Product model (DB migration)
- Auto-populated during STEP processing (non-fatal, 10s timeout)
- Also stored in cad_files.mesh_attributes["rich_metadata"]
- Batch re-extract endpoint: POST /admin/settings/reextract-rich-metadata

AI Agent:
- search_products returns part_count, volume_cm3, complexity, largest_part
- query_database tool description documents cad_metadata schema

Frontend:
- ProductDetail page: CAD Metadata section with stat cards
  (parts, volume, surface area, complexity, triangles, assembly depth)
- Admin System Tools: "Re-extract Rich Metadata" button for backfill

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/Admin.tsx

@@ -179,6 +179,14 @@ export default function AdminPage() {
     onError: (e: any) => toast.error(e.response?.data?.detail || 'Failed'),
   })
 
+  const reextractRichMetadataMut = useMutation({
+    mutationFn: () => api.post('/admin/settings/reextract-rich-metadata'),
+    onSuccess: (res) => {
+      toast.success(res.data.message || 'Rich metadata re-extraction queued')
+    },
+    onError: (e: any) => toast.error(e.response?.data?.detail || 'Failed'),
+  })
+
   const cleanupOrphanedCadMut = useMutation({
     mutationFn: () => api.post('/admin/settings/cleanup-orphaned-cad-files'),
     onSuccess: (res) => {
@@ -1228,6 +1236,21 @@ export default function AdminPage() {
                 </button>
               </div>
             </div>
+
+            <div className="card p-5">
+              <h3 className="text-sm font-semibold text-content mb-1">Re-extract Rich Metadata</h3>
+              <p className="text-xs text-content-muted mb-3">Re-compute volume, surface area, complexity for all products with STEP files.</p>
+              <div className="space-y-2">
+                <button
+                  onClick={() => reextractRichMetadataMut.mutate()}
+                  disabled={reextractRichMetadataMut.isPending}
+                  className="btn-secondary text-sm w-full justify-start"
+                >
+                  <RefreshCw size={14} className={reextractRichMetadataMut.isPending ? 'animate-spin' : ''} />
+                  {reextractRichMetadataMut.isPending ? 'Queueing...' : 'Re-extract Rich Metadata'}
+                </button>
+              </div>
+            </div>
           </div>
         </div>