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/job_registry.py

@@ -0,0 +1,60 @@
+"""
+Job Registry — decouples ARQ worker from direct plugin imports.
+
+Plugins register their job functions via register_job() at import time.
+The worker retrieves all registered jobs via get_all_jobs() instead of
+importing from plugin modules directly.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Any, Callable, Coroutine
+
+logger = logging.getLogger(__name__)
+
+# Type alias for an async job function
+JobFunc = Callable[..., Coroutine[Any, Any, Any]]
+
+# Internal registry: name -> job function
+_registry: dict[str, JobFunc] = {}
+
+
+def register_job(name: str, func: JobFunc) -> None:
+    """Register a job function under the given name.
+
+    Args:
+        name: Unique job name (e.g. 'index_mails').
+        func: The async callable to register.
+    """
+    if name in _registry:
+        logger.warning("Job '%s' is being re-registered — overwriting", name)
+    _registry[name] = func
+    logger.debug("Registered job: %s", name)
+
+
+def get_job(name: str) -> JobFunc | None:
+    """Retrieve a registered job function by name.
+
+    Args:
+        name: The job name to look up.
+
+    Returns:
+        The registered callable, or None if not found.
+    """
+    return _registry.get(name)
+
+
+def get_all_jobs() -> list[JobFunc]:
+    """Return all registered job functions (order is insertion order).
+
+    Returns:
+        List of all registered async callables.
+    """
+    return list(_registry.values())
+
+
+def clear_registry() -> None:
+    """Clear all registered jobs. Useful for testing."""
+    _registry.clear()
+    logger.debug("Job registry cleared")