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/components/cad/cadUtils.ts

@@ -0,0 +1,87 @@
+import type { PartMaterialEntry, PartMaterialMap } from '../../api/cad'
+
+/**
+ * Normalize a GLB mesh name by stripping suffixes added by the export pipeline:
+ * - OCC RWGltf_CafWriter adds "_AF0", "_AF1", … for repeated assembly instances
+ * - Blender adds ".001", ".002", … for name deduplication on re-import
+ *
+ * Mirrors the logic in render-worker/scripts/export_gltf.py (lines 107-114).
+ *
+ * Examples:
+ *   "Ring_AF3"                       → "Ring"
+ *   "Ring_AF0_AF1"                   → "Ring"   (nested suffixes — loop until stable)
+ *   "Cage.001"                       → "Cage"
+ *   "Cage.001_AF2"                   → "Cage"
+ *   "KOMP_ASM_1_AF0_ASM"             → "KOMP_ASM_1"  (_AF0_ASM variant)
+ *   "GE360-HF_000_P_ASM_1_AF0_ASM"  → "GE360-HF_000_P_ASM_1"
+ *   "PlainPart"                      → "PlainPart"
+ */
+export function normalizeMeshName(name: string): string {
+  // Strip Blender dedup suffix (.001, .002, …)
+  let n = name.replace(/\.\d{3}$/, '')
+  // Strip OCC assembly-instance suffix — handles _AF0, _AF1, _AF0_ASM, _AF1_ASM patterns
+  // The optional (_ASM)? group catches assembly-node variants like _AF0_ASM
+  let prev = ''
+  while (prev !== n) { prev = n; n = n.replace(/_AF\d+(_ASM)?$/i, '') }
+  return n
+}
+
+// ---------------------------------------------------------------------------
+// resolvePartMaterial
+// ---------------------------------------------------------------------------
+
+/**
+ * Resolve a material entry for a (already-normalized) GLB mesh name.
+ *
+ * OCC's GLB exporter strips certain path suffixes (_ASM_1, _1, _AF\d+_\d+)
+ * that cadquery keeps when parsing the STEP topology. This means stored keys
+ * from Excel-imported cad_part_materials may have extra suffixes compared to
+ * the actual GLB mesh names.
+ *
+ * Strategy:
+ *  1. Exact match: partMaterials[meshKey]
+ *  2. Prefix match: find shortest stored key that starts with meshKey + '_'
+ *     e.g. GLB "GE360-EIN_HAELFTE" matches stored "GE360-EIN_HAELFTE_AF0_1"
+ *
+ * Returns undefined when no match exists.
+ */
+export function resolvePartMaterial(
+  meshKey: string,
+  partMaterials: PartMaterialMap,
+): PartMaterialEntry | undefined {
+  // 1. Exact match
+  if (partMaterials[meshKey]) return partMaterials[meshKey]
+  // 2. Shortest stored key that starts with meshKey + '_'
+  let bestKey: string | undefined
+  for (const key of Object.keys(partMaterials)) {
+    if (key.startsWith(meshKey + '_')) {
+      if (!bestKey || key.length < bestKey.length) bestKey = key
+    }
+  }
+  return bestKey ? partMaterials[bestKey] : undefined
+}
+
+// ---------------------------------------------------------------------------
+// convertCadPartMaterials
+// ---------------------------------------------------------------------------
+
+/**
+ * Convert Product.cad_part_materials (list of {part_name, material}) to
+ * the PartMaterialMap format used by the 3D viewers.
+ *
+ * - Skips entries with blank part_name or material
+ * - Detects hex colors (starting with "#") vs library material names
+ * - Normalizes part names with normalizeMeshName() so they match GLB mesh keys
+ */
+export function convertCadPartMaterials(
+  items: Array<{ part_name: string; material: string }>,
+): PartMaterialMap {
+  const result: PartMaterialMap = {}
+  for (const item of items) {
+    if (!item.part_name.trim() || !item.material.trim()) continue
+    const key = normalizeMeshName(item.part_name.trim())
+    const value = item.material.trim()
+    result[key] = { type: value.startsWith('#') ? 'hex' : 'library', value }
+  }
+  return result
+}