feat: sharp edge pipeline V02, tessellation presets, media cache-bust, GMSH plan

Sharp Edge Pipeline V02:
- export_step_to_gltf.py: replace BRep_Tool.Polygon3D_s (returns None in XCAF) with
  GCPnts_UniformAbscissa curve sampling at 0.3mm step — extracts 17,129 segment pairs
- Inject sharp_edge_pairs + sharp_threshold_deg into GLB extras (scenes[0].extras)
  via binary GLB JSON-chunk patching (no extra dependency)
- export_gltf.py: read schaeffler_sharp_edge_pairs from Blender scene custom props,
  apply via KD-tree to mark edges sharp=True + seam=True (OCC mm Z-up → Blender transform)
- tools/restore_sharp_marks.py: dual-pass (dihedral angle + OCC pairs), updated coordinate
  transform (X, -Z, Y) * 0.001

Tessellation:
- Admin UI: Draft / Standard / Fine preset buttons with active-state highlighting
- Default angular deflection: preview 0.5→0.1 rad, production 0.2→0.05 rad
- export_glb.py: read updated defaults from system_settings

Media / Cache:
- media/service.py: get_download_url appends ?v={file_size_bytes} cache-buster
- media/router.py: Cache-Control: no-cache for all download/thumbnail endpoints

Render pipeline:
- still_render.py / turntable_render.py: shared GPU activation + camera improvements
- render_order_line.py: global render position support
- render_thumbnail.py: updated defaults

Frontend:
- InlineCadViewer: file_size_bytes-aware URL update triggers re-fetch on regeneration
- ThreeDViewer: material panel, part selection, PBR mode improvements
- Admin.tsx: tessellation preset cards, GMSH setting dropdown
- MediaBrowser, ProductDetail, OrderDetail, Orders: various UI improvements
- New: MaterialPanel, GlobalRenderPositionsPanel, StepIndicator components
- New: renderPositions.ts API client

Plans / Docs:
- plan.md: GMSH Frontal-Delaunay tessellation plan (6 tasks)
- LEARNINGS.md: OCC Polygon3D_s None issue + GCPnts fix
- .gitignore: add backend/core (core dump from root process)

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

backend/app/api/routers/admin.py

@@ -43,9 +43,9 @@ SETTINGS_DEFAULTS: dict[str, str] = {
     "smtp_from_address":               "",
     # glTF tessellation quality (OCC BRepMesh)
     "gltf_preview_linear_deflection":      "0.1",   # mm — geometry GLB for viewer
-    "gltf_preview_angular_deflection":     "0.5",   # rad
+    "gltf_preview_angular_deflection":     "0.1",   # rad — Standard preset
     "gltf_production_linear_deflection":   "0.03",  # mm — production GLB
-    "gltf_production_angular_deflection":  "0.2",   # rad
+    "gltf_production_angular_deflection":  "0.05",  # rad — Standard preset
     # 3D viewer / glTF export settings
     "gltf_scale_factor":               "0.001",
     "gltf_smooth_normals":             "true",
@@ -77,9 +77,9 @@ class SettingsOut(BaseModel):
     smtp_password: str = ""
     smtp_from_address: str = ""
     gltf_preview_linear_deflection: float = 0.1
-    gltf_preview_angular_deflection: float = 0.5
+    gltf_preview_angular_deflection: float = 0.1
     gltf_production_linear_deflection: float = 0.03
-    gltf_production_angular_deflection: float = 0.2
+    gltf_production_angular_deflection: float = 0.05
     gltf_scale_factor: float = 0.001
     gltf_smooth_normals: bool = True
     viewer_max_distance: float = 50.0
@@ -420,9 +420,12 @@ async def regenerate_thumbnails(
     admin: User = Depends(require_admin),
     db: AsyncSession = Depends(get_db),
 ):
-    """Re-queue all completed CAD files for thumbnail regeneration."""
+    """Re-queue completed CAD files that are linked to a product for thumbnail regeneration."""
+    from app.domains.products.models import Product
     result = await db.execute(
-        select(CadFile).where(CadFile.processing_status == ProcessingStatus.completed)
+        select(CadFile)
+        .join(Product, Product.cad_file_id == CadFile.id)
+        .where(CadFile.processing_status == ProcessingStatus.completed)
     )
     cad_files = result.scalars().all()
 
@@ -435,6 +438,71 @@ async def regenerate_thumbnails(
     return {"queued": queued, "message": f"Re-queued {queued} CAD file(s) for thumbnail regeneration"}
 
 
+@router.get("/settings/orphaned-cad-files")
+async def get_orphaned_cad_files(
+    admin: User = Depends(require_admin),
+    db: AsyncSession = Depends(get_db),
+):
+    """Return count and total disk size of CadFiles not linked to any product."""
+    from sqlalchemy import func
+    from app.domains.products.models import Product
+    result = await db.execute(
+        select(func.count(CadFile.id), func.sum(CadFile.file_size))
+        .outerjoin(Product, Product.cad_file_id == CadFile.id)
+        .where(Product.id.is_(None))
+    )
+    count, total_bytes = result.one()
+    return {
+        "count": count or 0,
+        "total_mb": round((total_bytes or 0) / 1024 / 1024, 1),
+    }
+
+
+@router.post("/settings/cleanup-orphaned-cad-files")
+async def cleanup_orphaned_cad_files(
+    admin: User = Depends(require_admin),
+    db: AsyncSession = Depends(get_db),
+):
+    """Delete CadFile DB records and associated files on disk for all orphaned CadFiles.
+
+    A CadFile is orphaned if no product currently references it via products.cad_file_id.
+    """
+    import os
+    from app.domains.products.models import Product
+
+    result = await db.execute(
+        select(CadFile)
+        .outerjoin(Product, Product.cad_file_id == CadFile.id)
+        .where(Product.id.is_(None))
+    )
+    orphans = result.scalars().all()
+
+    deleted_files = 0
+    deleted_bytes = 0
+
+    for cad_file in orphans:
+        # Remove files from disk (non-fatal if missing)
+        for path_attr in ("stored_path", "thumbnail_path", "gltf_path"):
+            path = getattr(cad_file, path_attr, None)
+            if path:
+                try:
+                    if os.path.isfile(path):
+                        size = os.path.getsize(path)
+                        os.remove(path)
+                        deleted_files += 1
+                        deleted_bytes += size
+                except OSError:
+                    pass
+        await db.delete(cad_file)
+
+    await db.commit()
+    return {
+        "deleted_records": len(orphans),
+        "deleted_files": deleted_files,
+        "freed_mb": round(deleted_bytes / 1024 / 1024, 1),
+    }
+
+
 @router.post("/settings/reextract-metadata", status_code=status.HTTP_202_ACCEPTED)
 async def reextract_all_metadata(
     admin: User = Depends(require_admin),
@@ -445,8 +513,11 @@ async def reextract_all_metadata(
     Updates mesh_attributes without re-rendering thumbnails or changing processing status.
     Use this after deploying bbox/edge extraction improvements.
     """
+    from app.domains.products.models import Product
     result = await db.execute(
-        select(CadFile).where(
+        select(CadFile)
+        .join(Product, Product.cad_file_id == CadFile.id)
+        .where(
             CadFile.processing_status == ProcessingStatus.completed,
             CadFile.stored_path.isnot(None),
         )