feat(backend): setup FastAPI + SQLite + config

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -0,0 +1,33 @@
+import os
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from app.config import CORS_ORIGINS, UPLOAD_DIR
+from app.database import create_db_and_tables
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    os.makedirs(UPLOAD_DIR, exist_ok=True)
+    import app.models  # noqa — enregistre tous les modèles avant create_all
+    create_db_and_tables()
+    from app.seed import run_seed
+    run_seed()
+    yield
+
+
+app = FastAPI(title="Jardin API", lifespan=lifespan)
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=CORS_ORIGINS,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+
+@app.get("/api/health")
+def health():
+    return {"status": "ok"}