feat: mail phase 4 - IMAP folder create/delete + auto-sync

- Add imap_create_folder() and imap_delete_folder() service functions
- Call IMAP CREATE/DELETE in folder create/delete endpoints
- Add auto_sync_all_accounts() background task (every 5 min)
- Start auto-sync loop on plugin activation via asyncio.create_task
- Frontend: working sync button with isSyncing state and toast feedback
- i18n: syncSuccess, syncFailed, syncing, autoSyncEnabled keys (de/en)

app/plugins/builtins/mail/plugin.py

@@ -2,13 +2,32 @@
 
 from __future__ import annotations
 
+import asyncio
+import logging
+
 from app.plugins.base import BasePlugin
 from app.plugins.manifest import PluginManifest, PluginRouteDef
 
+logger = logging.getLogger(__name__)
+
+
+async def _auto_sync_loop() -> None:
+    """Background loop: sync all active mail accounts every 5 minutes."""
+    from app.plugins.builtins.mail.services import auto_sync_all_accounts
+
+    while True:
+        try:
+            await auto_sync_all_accounts()
+        except Exception as exc:
+            logger.warning("auto_sync error: %s", exc)
+        await asyncio.sleep(300)
+
 
 class MailPlugin(BasePlugin):
     """Mail plugin for email management: IMAP sync, SMTP send, threading, rules, PGP."""
 
+    _auto_sync_task: asyncio.Task | None = None
+
     manifest = PluginManifest(
         name="mail",
         version="1.0.0",
@@ -29,3 +48,28 @@ class MailPlugin(BasePlugin):
         migrations=["0001_initial.sql"],
         permissions=[],
     )
+
+    async def on_activate(
+        self, db, service_container, event_bus
+    ) -> None:
+        """Activate plugin: register events + start auto-sync background task."""
+        await super().on_activate(db, service_container, event_bus)
+
+        if self._auto_sync_task is None or self._auto_sync_task.done():
+            self._auto_sync_task = asyncio.create_task(_auto_sync_loop())
+            logger.info("Mail plugin: auto-sync background task started")
+
+    async def on_deactivate(
+        self, db, service_container, event_bus
+    ) -> None:
+        """Deactivate plugin: stop auto-sync task + unregister events."""
+        if self._auto_sync_task is not None and not self._auto_sync_task.done():
+            self._auto_sync_task.cancel()
+            try:
+                await self._auto_sync_task
+            except asyncio.CancelledError:
+                pass
+            self._auto_sync_task = None
+            logger.info("Mail plugin: auto-sync background task stopped")
+
+        await super().on_deactivate(db, service_container, event_bus)