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/domains/pipeline/tasks/render_order_line.py

@@ -130,7 +130,7 @@ def render_order_line_task(self, order_line_id: str):
                 logger.info(f"No render template for category_key={category_key!r}, output_type_id={ot_id!r}")
 
             cad_name = cad_file.original_name if cad_file else "?"
-            # Load render_position for rotation values
+            # Load render_position for rotation values (per-product takes priority, falls back to global)
             rotation_x = rotation_y = rotation_z = 0.0
             if line.render_position_id:
                 from app.models.render_position import ProductRenderPosition
@@ -138,6 +138,12 @@ def render_order_line_task(self, order_line_id: str):
                 if rp:
                     rotation_x, rotation_y, rotation_z = rp.rotation_x, rp.rotation_y, rp.rotation_z
                     emit(order_line_id, f"Render position: '{rp.name}' ({rotation_x}°, {rotation_y}°, {rotation_z}°)")
+            elif line.global_render_position_id:
+                from app.models import GlobalRenderPosition
+                grp = session.get(GlobalRenderPosition, line.global_render_position_id)
+                if grp:
+                    rotation_x, rotation_y, rotation_z = grp.rotation_x, grp.rotation_y, grp.rotation_z
+                    emit(order_line_id, f"Global render position: '{grp.name}' ({rotation_x}°, {rotation_y}°, {rotation_z}°)")
 
             emit(order_line_id, f"Starting render for {cad_name} ({len(part_colors)} coloured parts)")
 
@@ -345,6 +351,7 @@ def render_order_line_task(self, order_line_id: str):
             if success:
                 # Create MediaAsset so the render appears in the Media Browser
                 try:
+                    import os as _os
                     from app.domains.media.models import MediaAsset, MediaAssetType as MAT
                     from app.config import settings as _cfg2
                     _ext = str(output_path).rsplit(".", 1)[-1].lower() if "." in str(output_path) else "bin"
@@ -360,6 +367,33 @@ def render_order_line_task(self, order_line_id: str):
                         select(MediaAsset.id).where(MediaAsset.storage_key == _norm_key).limit(1)
                     ).scalar_one_or_none()
                     if not _existing:
+                        # Probe output file for metadata
+                        _file_size = None
+                        _width = None
+                        _height = None
+                        if _os.path.exists(output_path):
+                            try:
+                                _file_size = _os.path.getsize(output_path)
+                            except OSError:
+                                pass
+                            if _ext in ("png", "jpg", "jpeg"):
+                                try:
+                                    from PIL import Image as _PILImage
+                                    with _PILImage.open(output_path) as _im:
+                                        _width, _height = _im.size
+                                except Exception:
+                                    pass
+                        # Snapshot key render settings into render_config
+                        _render_config = None
+                        if isinstance(render_log, dict):
+                            _render_config = {
+                                k: render_log[k]
+                                for k in (
+                                    "renderer", "engine_used", "engine", "samples",
+                                    "device_used", "compute_type", "total_duration_s",
+                                )
+                                if k in render_log
+                            }
                         _asset = MediaAsset(
                             tenant_id=_tenant_id,
                             order_line_id=line.id,
@@ -367,6 +401,10 @@ def render_order_line_task(self, order_line_id: str):
                             asset_type=_at,
                             storage_key=_norm_key,
                             mime_type=_mime,
+                            file_size_bytes=_file_size,
+                            width=_width,
+                            height=_height,
+                            render_config=_render_config,
                         )
                         session.add(_asset)
                         session.commit()