feat: notification preferences system with plugin registry

- Add NotificationType and NotificationPreference models
- Add get_notification_types() to BasePlugin for plugin registration
- Add sync_notification_types() to PluginRegistry
- Update create_notification() to check user preferences (returns Notification|None)
- Add API endpoints: GET /types, GET /preferences, PATCH /preferences/{type_key}
- Add NotificationPreferenceUpdate schema
- Mail plugin registers 10 notification types with metadata
- Add Alembic migration 0017 for new tables + seed data
- Frontend: SettingsNotifications page with toggle switches
- Frontend: Settings tab, route, hooks for notification preferences
- i18n: notification settings keys (de/en)

app/plugins/registry.py

@@ -117,6 +117,73 @@ class PluginRegistry:
         """List all discovered plugin names."""
         return list(self._plugins.keys())
 
+    # ── Notification Type Sync ──
+
+    async def sync_notification_types(self, db: AsyncSession) -> None:
+        """Sync notification types from all active plugins to DB.
+
+        For each active plugin, calls get_notification_types() and upserts
+        the returned types into the notification_types table. Removes types
+        belonging to plugins that are no longer active.
+        """
+        from app.models.notification import NotificationType
+
+        # Collect all notification types from active plugins
+        active_types: dict[str, dict[str, Any]] = {}  # type_key -> type_data
+        for name, plugin in self._plugins.items():
+            record = await self._get_plugin_record(db, name)
+            if record is None or not record.active:
+                continue
+            for nt in plugin.get_notification_types():
+                key = nt.get("type_key", "")
+                if not key:
+                    continue
+                active_types[key] = {
+                    "type_key": key,
+                    "plugin_name": name,
+                    "category": nt.get("category", "general"),
+                    "label": nt.get("label", key),
+                    "description": nt.get("description"),
+                    "is_enabled_by_default": nt.get("is_enabled_by_default", True),
+                }
+
+        # Fetch existing types from DB
+        result = await db.execute(select(NotificationType))
+        existing = {row.type_key: row for row in result.scalars().all()}
+
+        # Upsert active types
+        for key, data in active_types.items():
+            if key in existing:
+                row = existing[key]
+                row.plugin_name = data["plugin_name"]
+                row.category = data["category"]
+                row.label = data["label"]
+                row.description = data["description"]
+                row.is_enabled_by_default = data["is_enabled_by_default"]
+            else:
+                new_row = NotificationType(
+                    type_key=key,
+                    plugin_name=data["plugin_name"],
+                    category=data["category"],
+                    label=data["label"],
+                    description=data["description"],
+                    is_enabled_by_default=data["is_enabled_by_default"],
+                )
+                db.add(new_row)
+
+        # Remove types from plugins that are no longer active
+        active_keys = set(active_types.keys())
+        for key, row in existing.items():
+            if key not in active_keys:
+                # Check if the plugin is still active
+                plugin_name = row.plugin_name
+                plugin_record = await self._get_plugin_record(db, plugin_name)
+                if plugin_record is None or not plugin_record.active:
+                    await db.delete(row)
+
+        await db.flush()
+        logger.info("Synced %d notification types from active plugins", len(active_types))
+
     # ── DB Status Sync ──
 
     async def sync_db_status(self, db: AsyncSession) -> None:
@@ -418,6 +485,9 @@ class PluginRegistry:
                         mounted_routes.append(r)
             self._mounted_routes[name] = mounted_routes
 
+        # Sync notification types from this plugin
+        await self.sync_notification_types(db)
+
         # Update DB record
         record.status = "active"
         record.active = True