Docker : supprime alembic upgrade head du startup

Le lifespan FastAPI appelle déjà init_db() (create_all) au démarrage.
Lancer alembic en plus cassait sur une DB vide (migration initiale manquante).

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

docker/backend.Dockerfile

@@ -32,7 +32,7 @@ EXPOSE 8002
 HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
     CMD curl -f http://localhost:8002/api/health || exit 1
 
-CMD ["sh", "-c", "alembic upgrade head && uvicorn app.main:app --host 0.0.0.0 --port 8002"]
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8002"]
 
 # ── Development ───────────────────────────────────────────────────────────────
 FROM base AS development
@@ -41,4 +41,4 @@ COPY backend/requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
 WORKDIR /app
-CMD ["sh", "-c", "alembic upgrade head && uvicorn app.main:app --host 0.0.0.0 --port 8002 --reload"]
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8002", "--reload"]