Implement Deprecation Warning System and Router Registry Cleanup

- Added DeprecationParams dependency to log warnings when legacy routes are accessed.
- Updated setup_routers to apply deprecation warnings to non-V3 legacy endpoints.
- Exempted core infrastructure, special routers, and routers currently in use from deprecation warnings.
- Cleaned up 24 unused router imports from the registry.

app/routers/dependencies_v3.py

@@ -1,4 +1,4 @@
-from fastapi import Depends, Header, HTTPException, Query, Response, status
+from fastapi import Depends, Header, HTTPException, Query, Request, Response, status
 from typing import Optional, Union
 import logging
 import asyncio
@@ -7,6 +7,13 @@ from app.models.auth_models import AccountContext
 
 log = logging.getLogger(__name__)
 
+# --- Deprecation Dependency ---
+
+class DeprecationParams:
+    """Logs a warning when a legacy/deprecated route is accessed."""
+    def __init__(self, request: Request):
+        log.warning(f"!!! DEPRECATED ROUTE ACCESSED: [{request.method}] {request.url.path} from {request.client.host if request.client else 'Unknown'}")
+
 # --- Account Context Dependencies ---
 
 def get_account_context_optional(