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

package.py

@@ -0,0 +1,17 @@
+"""AYON Addon: Matrix Publish — sends published products to Matrix rooms."""
+
+name = "matrix_publish"
+title = "Matrix Publish"
+version = "0.1.0"
+client_dir = "ayon_matrix_publish"
+
+# Services needed
+services = {}
+
+# Ayon dependency
+ayon_required_addons = {
+    "core": ">=1.0.0"
+}
+
+# Plugin paths
+ayon_compatible_addons = {}