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/config.py

@@ -12,6 +12,7 @@ class Settings(BaseSettings):
     # Application
     APP_NAME: str = "Imago"
     APP_VERSION: str = "1.0.0"
+    API_V1_SUNSET_DATE: str = ""
     DEBUG: bool = False
     SECRET_KEY: str = "changez-moi"
 
@@ -84,6 +85,7 @@ class Settings(BaseSettings):
     S3_BUCKET: str = ""
     S3_REGION: str = "us-east-1"
     S3_ENDPOINT_URL: str = ""               # vide = AWS, sinon MinIO/R2
+    S3_ENDPOINT_PUBLIC: str = ""            # URL utilisée pour les liens présignés (ex: http://localhost:9000)
     S3_ACCESS_KEY: str = ""
     S3_SECRET_KEY: str = ""
     S3_PREFIX: str = "imago"