Add local Modly 3D generation integration

Problem

Blender MCP currently supports cloud-backed 3D generation through Hyper3D Rodin and Hunyuan3D, but it has no integration for local, offline generation through Modly.

Proposed solution

Add an optional Modly integration that talks to the running Modly desktop API using its canonical workflow-run contract.

• Configure and validate a Modly API base URL in the Blender add-on (default: http://127.0.0.1:8765).
• Expose status/model discovery to MCP clients.
• Start image-to-3D jobs through POST /workflow-runs/from-image.
• Poll jobs through GET /workflow-runs/{run_id}.
• Export completed workspace meshes as GLB and import them into Blender.
• Keep the root addon.py and packaged src/blender_mcp/bundled/addon.py synchronized.
• Document setup and environment-variable configuration.
• Add regression tests for request routing, path validation, and imports.

Acceptance criteria

• Modly is opt-in and disabled by default.
• A user can point Blender MCP at a local or LAN Modly instance.
• The MCP flow covers status, model listing, image generation, polling, and Blender import.
• Invalid or traversal-style workspace paths are rejected before export.
• Existing integrations and tests continue to pass.