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/core/storage.py

@@ -19,6 +19,8 @@ import os
 from abc import ABC, abstractmethod
 from typing import Any
 
+import aiofiles
+
 logger = logging.getLogger(__name__)
 
 
@@ -70,15 +72,15 @@ class LocalStorage(StorageBackend):
     async def save(self, path: str, data: bytes) -> str:
         full_path = self._full_path(path)
         os.makedirs(os.path.dirname(full_path), exist_ok=True)
-        with open(full_path, "wb") as f:
-            f.write(data)
+        async with aiofiles.open(full_path, "wb") as f:
+            await f.write(data)
         logger.debug("LocalStorage: saved %s (%d bytes)", path, len(data))
         return path
 
     async def read(self, path: str) -> bytes:
         full_path = self._full_path(path)
-        with open(full_path, "rb") as f:
-            return f.read()
+        async with aiofiles.open(full_path, "rb") as f:
+            return await f.read()
 
     async def delete(self, path: str) -> bool:
         full_path = self._full_path(path)