Initial commit: AYON Matrix Publish addon

- package.py: addon manifest (v0.1.0)
- server/__init__.py: BaseServerAddon definition
- server/ayon_matrix_publish/plugins/publish/integrate_matrix.py:
  Pyblish plugin that uploads published representations to Matrix
  rooms during the Integration stage. Supports:
  - Upload to Matrix content repository (mxc:// URI)
  - Formatted messages with preview images
  - Auto room creation per asset
  - Configurable via Studio Settings or env vars
- create_package.py: builds distributable .zip package

client/ayon_matrix_publish/__init__.py

@@ -0,0 +1,2 @@
+# -*- coding: utf-8 -*-
+"""Matrix Publish addon — client-side (DCC host)."""

client/ayon_matrix_publish/plugins/publish/__init__.py

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+# -*- coding: utf-8 -*-
+"""Client-side plugins for Matrix Publish.
+
+These plugins run inside the DCC host (Maya, Houdini, Nuke, etc.)
+and are discovered by AYON's Pyblish plugin loader.
+
+The publish plugin lives in ayon_matrix_publish/plugins/publish/.
+"""
+
+from ayon_core.pipeline import publish
+
+# Import the plugin so Pyblish discovers it
+from .plugins.publish.integrate_matrix import IntegrateMatrix
+
+__all__ = ["IntegrateMatrix"]