feat: add Matrix chat notification support (#211)

Implements native Matrix notification channel support, allowing users
to receive service alerts in any Matrix room via the Client-Server API.

Changes:
- server/service-operation/notification/matrix.go: new Matrix service
  implementing the NotificationService interface (PUT /_matrix/client/v3/...)
- server/service-operation/notification/types.go: add MatrixHomeserver,
  MatrixRoomID, MatrixAccessToken fields to AlertConfiguration
- server/service-operation/notification/manager.go: register MatrixService
- server/pb_migrations/1772200000_updated_alert_configurations_matrix.js:
  PocketBase migration adding matrix fields and notification_type value
- application: Matrix option in channel dialog with homeserver/room/token
  fields, tab filter, list display, type definitions and translations (en, km)
- application/public/upload/notification/matrix.png: Matrix channel icon

server/pb_migrations/1772200000_updated_alert_configurations_matrix.js

@@ -0,0 +1,73 @@
+/// <reference path="../pb_data/types.d.ts" />
+migrate((app) => {
+  const collection = app.findCollectionByNameOrId("pbc_1938176441")
+
+  // add matrix_homeserver field
+  collection.fields.addAt(collection.fields.length, new Field({
+    "autogeneratePattern": "",
+    "hidden": false,
+    "id": "text_matrix_homeserver",
+    "max": 0,
+    "min": 0,
+    "name": "matrix_homeserver",
+    "pattern": "",
+    "presentable": false,
+    "primaryKey": false,
+    "required": false,
+    "system": false,
+    "type": "text"
+  }))
+
+  // add matrix_room_id field
+  collection.fields.addAt(collection.fields.length, new Field({
+    "autogeneratePattern": "",
+    "hidden": false,
+    "id": "text_matrix_room_id",
+    "max": 0,
+    "min": 0,
+    "name": "matrix_room_id",
+    "pattern": "",
+    "presentable": false,
+    "primaryKey": false,
+    "required": false,
+    "system": false,
+    "type": "text"
+  }))
+
+  // add matrix_access_token field
+  collection.fields.addAt(collection.fields.length, new Field({
+    "autogeneratePattern": "",
+    "hidden": false,
+    "id": "text_matrix_access_token",
+    "max": 0,
+    "min": 0,
+    "name": "matrix_access_token",
+    "pattern": "",
+    "presentable": false,
+    "primaryKey": false,
+    "required": false,
+    "system": false,
+    "type": "text"
+  }))
+
+  // add "matrix" to the notification_type select field values
+  const notifTypeField = collection.fields.getByName("notification_type")
+  if (notifTypeField && notifTypeField.values) {
+    notifTypeField.values.push("matrix")
+  }
+
+  return app.save(collection)
+}, (app) => {
+  const collection = app.findCollectionByNameOrId("pbc_1938176441")
+
+  collection.fields.removeById("text_matrix_homeserver")
+  collection.fields.removeById("text_matrix_room_id")
+  collection.fields.removeById("text_matrix_access_token")
+
+  const notifTypeField = collection.fields.getByName("notification_type")
+  if (notifTypeField && notifTypeField.values) {
+    notifTypeField.values = notifTypeField.values.filter(v => v !== "matrix")
+  }
+
+  return app.save(collection)
+})