UV and multi-material transfer fixes

IMPORTANT: Update BOTH the Blender addon and the Substance Painter plugin to 1.1.1. Re-export affected meshes from Blender and reload the FBX in Painter to establish matching UVs. Preserve the existing UV layout rather than recomputing it with Auto-unwrap.

- Exported meshes and returned textures use the same UV map, while preserving the original Blender mesh and UV order.

- Each material on the selected meshes exports its own images to the matching Painter texture set, independent of the selected set.

- Material transfer follows the connected shader through node groups and reroutes. Shared shader groups are isolated before editing.

- Repeated imports update the plugin-owned fill layer. Failed exports keep the previous complete mesh.

- Unsupported channels, missing UV maps, unmatched materials, and disabled Painter channels now produce diagnostics instead of silently reporting success.

- Creator buttons now open Omar Gamal's and Alexander Robertson's websites.

This is image-channel transfer, not shader baking. Computed shaders, packed channels, Mapping transforms, Bump-to-Normal conversion, and UDIM source images require baking to compatible separate images first.

Validation: Blender 5.2.2 tests and rendered before/after comparison passed. Painter routing was tested with API doubles; a live Painter session was not available.