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/mail/routes.py

@@ -884,7 +884,8 @@ async def list_threads(
             threads[tid] = {"thread_id": tid, "subject": mail.subject, "mail_count": 0, "mails": []}
         threads[tid]["mail_count"] += 1
         threads[tid]["mails"].append(mail_to_response(mail))
-    return list(threads.values())
+    items = list(threads.values())
+    return {"items": items, "total": len(items)}
 
 
 # ─── Templates (F-MAIL-06) ───

app/plugins/builtins/mail/services.py

@@ -1531,8 +1531,8 @@ async def send_mail_via_smtp(
         mime_type = att_info.get("mime_type", "application/octet-stream")
         if not file_path or not os.path.exists(file_path):
             continue
-        with open(file_path, "rb") as f:  # noqa: ASYNC230
-            content = f.read()
+        async with aiofiles.open(file_path, "rb") as f:
+            content = await f.read()
         # Determine maintype/subtype from mime_type
         if "/" in mime_type:
             maintype, subtype = mime_type.split("/", 1)