feat(P2): USD Foundation — canonical part identity + material overrides

M1 — USD exporter:
- render-worker/scripts/export_step_to_usd.py (631 lines)
  Full XCAF traversal, one UsdGeom.Mesh per leaf part,
  schaeffler:partKey on every prim, index-space sharpEdgeVertexPairs
- render-worker/Dockerfile: usd-core>=24.11 installed (USD 0.26.3)

M2 — usd_master MediaAsset + pipeline auto-chain:
- migrations 060 (usd_master enum), 061 (3 JSONB columns),
  062 (rename tessellation settings keys)
- generate_usd_master_task: runs export_step_to_usd.py, upserts
  usd_master MediaAsset, writes resolved_material_assignments to CadFile
- Auto-chained from generate_gltf_geometry_task after every GLB export
- step_tasks.py shim re-exports generate_usd_master_task

M3 — scene-manifest API:
- part_key_service.py: build_scene_manifest(), generate_part_key(),
  four-layer material priority resolution with provenance
- SceneManifest / PartEntry Pydantic models in products/schemas.py
- GET /api/cad/{id}/scene-manifest endpoint (graceful fallback to
  parsed_objects when USD not yet generated)
- POST /api/cad/{id}/generate-usd-master endpoint
- frontend/src/api/sceneManifest.ts: fetchSceneManifest(),
  triggerUsdMasterGeneration()

M4 — manual-material-overrides API:
- GET/PUT /api/cad/{id}/manual-material-overrides endpoints
- CadFile.manual_material_overrides JSONB column (migration 061)
- getManualOverrides() / saveManualOverrides() in cad.ts

M5 — ThreeDViewer partKey integration:
- export_step_to_gltf.py injects partKeyMap into GLB extras
- ThreeDViewer: partKeyMap extraction, resolvePartKey(), effectiveMaterials
  merges legacy partMaterials + new manualOverrides (server-side persistence)
- MaterialPanel: dual-path save (partKey vs legacy), provenance badge,
  reconciliation panel for unmatched/unassigned parts

Also:
- Admin.tsx: generate-missing-usd-masters + canonical scenes bulk actions
- ProductDetail.tsx: usd_master row in asset table
- vite-env.d.ts: fix ImportMeta.env TypeScript error
- GPUProbeResult: add timestamp/devices/render_time_s fields

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

render-worker/scripts/still_render.py

@@ -785,65 +785,6 @@ def main():
     bpy.ops.render.render(write_still=True)
     print("[still_render] render done.")
 
-    # ── Pillow post-processing: green bar + model name label ─────────────────
-    # Skip overlay for transparent renders to keep clean alpha channel
-    if transparent_bg:
-        print("[still_render] Transparent mode — skipping Pillow overlay.")
-    else:
-        try:
-            from PIL import Image, ImageDraw, ImageFont
-
-            img = Image.open(output_path).convert("RGBA")
-            draw = ImageDraw.Draw(img)
-            W, H = img.size
-
-            # Schaeffler green top bar
-            bar_h = max(8, H // 32)
-            draw.rectangle([0, 0, W - 1, bar_h - 1], fill=(0, 137, 61, 255))
-
-            # Model name strip at bottom
-            model_name = os.path.splitext(os.path.basename(glb_path))[0]
-            label_h = max(20, H // 20)
-            img.alpha_composite(
-                Image.new("RGBA", (W, label_h), (30, 30, 30, 180)),
-                dest=(0, H - label_h),
-            )
-
-            font_size = max(10, label_h - 6)
-            font = None
-            for fp in [
-                "/usr/share/fonts/truetype/dejavu/DejaVuSans-Bold.ttf",
-                "/usr/share/fonts/truetype/liberation/LiberationSans-Bold.ttf",
-                "/usr/share/fonts/truetype/freefont/FreeSansBold.ttf",
-            ]:
-                if os.path.exists(fp):
-                    try:
-                        font = ImageFont.truetype(fp, font_size)
-                        break
-                    except Exception:
-                        pass
-            if font is None:
-                font = ImageFont.load_default()
-
-            tb = draw.textbbox((0, 0), model_name, font=font)
-            text_w = tb[2] - tb[0]
-            draw.text(
-                ((W - text_w) // 2, H - label_h + (label_h - (tb[3] - tb[1])) // 2),
-                model_name, font=font, fill=(255, 255, 255, 255),
-            )
-
-            # Save in original format
-            if ext in ('.jpg', '.jpeg'):
-                img.convert("RGB").save(output_path, format="JPEG", quality=92)
-            else:
-                img.convert("RGB").save(output_path, format="PNG")
-            print("[still_render] Pillow overlay applied.")
-
-        except ImportError:
-            print("[still_render] Pillow not available - skipping overlay.")
-        except Exception as exc:
-            print(f"[still_render] Pillow overlay failed (non-fatal): {exc}")
-
     print("[still_render] Done.")