Add admin panel, WebSocket support, and API versioning

Introduce an admin portal (React + Nginx), WebSocket routing, and
API versioning middleware with `/api/v1/` prefix deprecation.
Add master API key authentication, new Prometheus metrics for AI
token consumption and active WebSockets, and extend S3 config
with a public endpoint URL. Update test paths and fixtures to
align with the new routing structure.

tests/test_storage_extended.py

@@ -1,6 +1,7 @@
 import pytest
 from fastapi import HTTPException
-from app.services.storage import save_upload, delete_files, get_image_url
+from app.services.storage import save_upload, delete_files
+from app.services.storage_backend import LocalStorage, S3Storage
 from unittest.mock import MagicMock, patch, AsyncMock
 import io
 
@@ -38,9 +39,8 @@ def test_delete_files_exists(tmp_path):
     assert not f1.exists()
     assert not f2.exists()
 
-def test_get_image_url():
-    url = get_image_url("img.jpg", "client1")
-    assert "/static/uploads/client1/img.jpg" in url
-    
-    thumb_url = get_image_url("img.jpg", "client1", thumb=True)
-    assert "/static/thumbnails/client1/img.jpg" in thumb_url
+@pytest.mark.asyncio
+async def test_get_signed_url():
+    storage = LocalStorage("/", "test_secret")
+    url = await storage.get_signed_url("uploads/client1/img.jpg")
+    assert url.startswith("/files/signed/")