Consolidate validation tools + generic agent naming.

- Consolidate mesh_health / overhangs / thin_walls / full_printability_check
  into a single blender_validate(checks=[...]) tool
- Rename internal _claude_ prefix to _agent_ for generic MCP support
  (backward-compatible fallbacks retained)
- Sync addon bl_info version to package version + drift guard
- Docs/MCP resources updated to reference blender_validate