Fix 3D modeling feedback: session context, CORS, and PNG workflow ...

- Embed session_id into the main system prompt so the model reliably
  sees the correct session files directory instead of hallucinating one.
- Add global CORS middleware to fix STL viewer iframe fetch errors.
- Switch modeler_3d PNG previews from content_publish to image_view
  so renders are debug-only for Navi, not user-facing cards.
- Remove literal {session_id} template from persona.txt.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Add 3D modeling profile with model_3d and render_3d tools ...

New profile:
- modeler_3d: 3D model design for 3D printing (OpenSCAD → STL)

New tools:
- model_3d: compile .scad → binary STL via OpenSCAD CLI
- render_3d: render PNG previews from STL (up to 3 views, 400×300)

Both tools return openscad_not_found error if OpenSCAD is not installed.

Docs:
- README.md: add modeler_3d to profile table
- docs/profiles.md: add modeler_3d to active profiles
- docs/tools.md: add model_3d and render_3d to builtin tools
- manuals/model_3d.md, manuals/render_3d.md: full usage manuals
- modeler_3d system_prompt.txt: OpenSCAD-first workflow with dedicated tools

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>