feat(api): redirect / to /docs so the HF Space App tab shows Swagger

Previously GET / returned 404 (no route defined), which made the
HuggingFace Space App tab look broken even though the API was healthy.
A 307 redirect to FastAPI's auto-generated Swagger UI gives any
browser visitor a usable landing page and a way to explore + try
endpoints with their API key.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/guichetoi/api/main.py

@@ -75,7 +75,7 @@ from pathlib import Path
 
 from fastapi import Depends, FastAPI, File, Header, HTTPException, Response, UploadFile, status
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import JSONResponse
+from fastapi.responses import JSONResponse, RedirectResponse
 
 from guichetoi import cms as cms_gen
 from guichetoi import recommendation as reco
@@ -257,6 +257,11 @@ def _require_engine(app: FastAPI):
 # ────────────────────────────────────────────────────────────────────────────
 # Routes
 # ────────────────────────────────────────────────────────────────────────────
+@app.get("/", include_in_schema=False)
+def root() -> RedirectResponse:
+    return RedirectResponse(url="/docs")
+
+
 @app.get("/health", tags=["meta"])
 def health() -> dict:
     """Liveness + readiness. Spring Boot polls this before routing traffic."""