feat: Add Matrix infrastructure (Synapse + Element Web)

- Synapse homeserver.yaml configuration
- Element Web config.json
- PostgreSQL init script for synapse DB
- Nginx gateway configuration
- Docker Compose for Matrix stack
- README_MATRIX.md documentation

infra/matrix/element-web/config.json

@@ -0,0 +1,57 @@
+{
+  "default_server_config": {
+    "m.homeserver": {
+      "base_url": "https://matrix.daarion.space",
+      "server_name": "daarion.space"
+    },
+    "m.identity_server": {
+      "base_url": "https://vector.im"
+    }
+  },
+  "brand": "DAARION",
+  "integrations_ui_url": "https://scalar.vector.im/",
+  "integrations_rest_url": "https://scalar.vector.im/api",
+  "integrations_widgets_urls": [
+    "https://scalar.vector.im/_matrix/integrations/v1",
+    "https://scalar.vector.im/api"
+  ],
+  "bug_report_endpoint_url": null,
+  "uisi_autorageshake_app": "element-auto-uisi",
+  "show_labs_settings": true,
+  "room_directory": {
+    "servers": [
+      "daarion.space"
+    ]
+  },
+  "enable_presence_by_hs_url": {
+    "https://matrix.daarion.space": true
+  },
+  "setting_defaults": {
+    "breadcrumbs": true,
+    "MessageComposerInput.showStickersButton": false
+  },
+  "features": {
+    "feature_spotlight": true
+  },
+  "default_country_code": "UA",
+  "default_theme": "dark",
+  "disable_custom_urls": false,
+  "disable_guests": true,
+  "disable_login_language_selector": false,
+  "disable_3pid_login": false,
+  "branding": {
+    "welcome_background_url": null,
+    "auth_header_logo_url": null,
+    "auth_footer_links": [
+      {
+        "text": "DAARION.city",
+        "url": "https://app.daarion.space"
+      }
+    ]
+  },
+  "embedded_pages": {
+    "welcome_url": null
+  },
+  "map_style_url": "https://api.maptiler.com/maps/streets/style.json?key=fU3vlMsMn4Jb6dnEIFsx"
+}
+