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.

app/dependencies/auth.py

@@ -62,6 +62,17 @@ async def verify_api_key(
             headers={"WWW-Authenticate": "Bearer"},
         )
 
+    # ── 1.5. Vérification Master Key (ADMIN_API_KEY) ───────
+    from app.config import settings
+    if settings.ADMIN_API_KEY and raw_key == settings.ADMIN_API_KEY:
+        # Retourne un client virtuel avec tous les droits
+        return APIClient(
+            id="admin-master",
+            name="Imago Master Admin",
+            scopes=["admin", "images:read", "images:write", "ai:use"],
+            plan="premium"
+        )
+
     # ── Lookup par hash ───────────────────────────────────────
     key_hash = hash_api_key(raw_key)
     result = await db.execute(