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>

frontend/src/index.css

@@ -79,6 +79,14 @@
   /* Status — Info */
   --color-status-info-bg: #dbeafe;
   --color-status-info-text: #1e40af;
+
+  /* Extended badge colors */
+  --color-badge-purple-bg: rgba(124, 58, 237, 0.1);
+  --color-badge-purple-text: #6d28d9;
+  --color-badge-orange-bg: rgba(234, 88, 12, 0.1);
+  --color-badge-orange-text: #c2410c;
+  --color-badge-teal-bg: rgba(13, 148, 136, 0.1);
+  --color-badge-teal-text: #0f766e;
 }
 
 /* ============================================================
@@ -117,6 +125,14 @@
   /* Status — Info */
   --color-status-info-bg: rgba(59, 130, 246, 0.15);
   --color-status-info-text: #60a5fa;
+
+  /* Extended badge colors */
+  --color-badge-purple-bg: rgba(124, 58, 237, 0.2);
+  --color-badge-purple-text: #a78bfa;
+  --color-badge-orange-bg: rgba(234, 88, 12, 0.2);
+  --color-badge-orange-text: #fb923c;
+  --color-badge-teal-bg: rgba(13, 148, 136, 0.2);
+  --color-badge-teal-text: #2dd4bf;
 }
 
 /* Dark accent-light overrides (rgba instead of solid pastel) */
@@ -230,6 +246,21 @@
     background-color: var(--color-bg-muted);
     color: var(--color-text-secondary);
   }
+  .badge-purple {
+    @apply badge;
+    background-color: var(--color-badge-purple-bg);
+    color: var(--color-badge-purple-text);
+  }
+  .badge-orange {
+    @apply badge;
+    background-color: var(--color-badge-orange-bg);
+    color: var(--color-badge-orange-text);
+  }
+  .badge-teal {
+    @apply badge;
+    background-color: var(--color-badge-teal-bg);
+    color: var(--color-badge-teal-text);
+  }
 
   /* Input base — replaces repeated inline input patterns */
   .input-base {