Migrate 3D modeling tools to standalone MCP server navi-3d ...

Phase 0 — Fix MCP error propagation:
- McpClient.call_tool now returns (output, is_error) tuple
- McpTool.execute sets success=False when MCP reports isError=True
- Fixes silent failures where MCP errors looked like success

Phase 1 — Create mcp-server-navi-3d:
- New standalone MCP server in mcp-servers/navi-3d/
- Tools: compile_scad, render_stl, lint_scad
- Session-scoped path resolution via SESSION_FILES_DIR env
- Anti-escape validation for security
- Includes tests/unit/test_scad_analyze.py

Phase 2 — Remove from Navi core:
- Deleted navi/tools/{model_3d,render_3d,scad_lint}.py
- Removed from registry.py builtins and navi/tools/__init__.py
- Updated pyproject.toml testpaths to exclude mcp-servers/

Phase 3 — Wire into Navi config:
- Added navi-3d block to mcp_servers.json (SSE on :8002)
- Updated modeler_3d profile: mcp_servers + updated system_prompt
- All old tool names replaced with mcp_navi-3d_* equivalents

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

Refine 3D modeler workflow

Simplify 3D SCAD subagent prompt

Relax 3D SCAD subagent constraints

Constrain 3D SCAD author subagents

Prioritize physical geometry in 3D profile

Delegate 3D SCAD authoring to subagents

Improve 3D modeling validation prompts

Add 3D modeling specification workflow

Improve 3D modeling workflow discipline

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>