perf: Fix all 7 code analysis issues

HIGH (Performance):
- Replace 8 sync file operations with aiofiles in async context (storage, mail,
  report_generator, dms_bridge, ai_assistant)
- Frontend bundle splitting: manualChunks for react-vendor, ui-components, tanstack,
  markdown, icons, utils, i18n (ui chunk 936K → ~19K)

MEDIUM (Architecture):
- Worker circular deps: Replace direct plugin imports with job_registry.py pattern
  (register_job/get_all_jobs, importlib-based lazy loading)
- App-wide ErrorBoundary: New ErrorBoundary.tsx component, wrapped in AppShell
  and all standalone routes

LOW (Code Quality):
- N+1 query fix: selectinload(Contact.contact_persons) in list_contacts()
- O(n²) dedup fix: SQL GROUP BY for email/phone duplicates, Dict-based name grouping
- Response format standardization: 7 routes converted from plain arrays to
  {items: [...], total: N} format

app/plugins/builtins/kommunikation/dms_bridge.py

@@ -7,6 +7,8 @@ import os
 import uuid
 from typing import Any
 
+import aiofiles
+
 from fastapi import UploadFile
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -117,8 +119,8 @@ class DmsBridge:
             f"{file_id}{file_ext}",
         )
         os.makedirs(os.path.dirname(storage_path), exist_ok=True)
-        with open(storage_path, "wb") as f:
-            f.write(content)
+        async with aiofiles.open(storage_path, "wb") as f:
+            await f.write(content)
 
         # Create DMS file record
         dms_file = DmsFile(