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_rate_limit.py

@@ -42,7 +42,7 @@ async def _quick_upload(async_client: AsyncClient, headers: dict) -> int:
 
     # Le pipeline ARQ est mocké globalement dans conftest.py
     response = await async_client.post(
-        "/images/upload",
+        "/api/v1/images/upload",
         files={"file": ("test.jpg", io.BytesIO(jpeg_bytes), "image/jpeg")},
         headers=headers,
     )
@@ -61,7 +61,7 @@ async def test_rate_limit_headers_present(
     # Le pipeline ARQ est mocké globalement dans conftest.py
     jpeg_bytes = b"\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x00\x00\x01\x00\x01\x00\x00\xff\xd9"
     response = await async_client.post(
-        "/images/upload",
+        "/api/v1/images/upload",
         files={"file": ("test.jpg", io.BytesIO(jpeg_bytes), "image/jpeg")},
         headers=auth_headers_a,
     )