feat: per-line render overrides — override any output type setting at order time

Instead of duplicating output types for every variation (WebP vs PNG,
different resolution), keep one canonical output type and override
specific fields per order line via render_overrides JSONB.

Backend:
- render_overrides JSONB column on OrderLine (DB migration)
- Render task merges overrides with output type settings (format, width,
  height, samples, engine, denoiser, transparent_bg, cycles_device)
- POST /orders/{id}/batch-render-overrides endpoint for bulk override
- PatchLineBody accepts render_overrides for per-line patching

Frontend:
- Batch render overrides section on OrderDetail: output format dropdown
  (PNG/JPG/WebP) + resolution dropdown (512-4096)
- Clear button to remove overrides

MCP:
- create_order tool: accepts product_ids, output_type, render_overrides,
  material_override — enables "render all products as WebP" via Claude
- set_render_overrides tool: batch override on existing orders

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

LEARNINGS.md

@@ -7,6 +7,9 @@
 
 ## Learnings
 
+### 2026-03-15 | Architecture | Per-order-line render overrides via JSONB
+Render overrides (JSONB) on OrderLine allow overriding any output type render setting (format, resolution, samples, engine, etc.) at order time without duplicating output types. Applied AFTER output type render_settings AND after transparent_bg/cycles_device_val assignment, so they take final priority. Also affects dispatch queue routing (width/height overrides change light vs heavy queue routing).
+
 ### 2026-03-14 | Blender | OBJ-Rotation Turntable: Reparenting von USD-Parts verschiebt Geometrie
 USD-importierte Parts haben existierende Eltern-Objekte (Xform-Nodes). `part.parent = pivot; part.matrix_parent_inverse = pivot.matrix_world.inverted()` verliert den Beitrag des alten Parents zur Welt-Position → Parts verschieben sich ~14m. Fix: World-Matrix vor Reparenting sichern, dann via `part.matrix_local = pivot.inverted() @ saved_world` wiederherstellen. Zusätzlich `bpy.context.view_layer.update()` vor dem Parenting aufrufen, damit `pivot.matrix_world` aktuell ist.