feat(backend): initialisation du projet FastAPI

Structure en couches api / services / repositories / models, sens de
dependance unique, une session SQLAlchemy async injectee par dependance.

- Python 3.14, dependances gerees par uv et verrouillees dans uv.lock
- FastAPI expose par une factory : aucune configuration lue a l'import,
  ce qui rend tests et migrations independants de l'environnement
- Settings Pydantic, APP_SECRET_KEY et DATABASE_URL sans valeur par defaut
- Sondes /health/live et /health/ready, metriques Prometheus sur /metrics
- Lint et format ruff, mypy strict, pytest avec couverture
- Alembic branche sur DATABASE_URL et non sur alembic.ini
- Image Docker multi-stage, utilisateur non root, sonde de sante integree

apps/backend/tests/api/test_health.py

@@ -0,0 +1,51 @@
+from collections.abc import AsyncIterator
+
+import pytest
+from fastapi import FastAPI
+from httpx import AsyncClient
+from sqlalchemy.exc import OperationalError
+
+from app.db.session import get_session
+
+
+async def test_liveness_exposes_service_metadata(client: AsyncClient) -> None:
+    response = await client.get("/api/v1/health/live")
+
+    assert response.status_code == 200
+    assert response.json() == {
+        "status": "ok",
+        "service": "EnerVision API",
+        "version": "0.1.0",
+        "environment": "local",
+    }
+
+
+@pytest.mark.parametrize(
+    "failure",
+    [
+        OperationalError("SELECT 1", {}, Exception("connexion refusee")),
+        ConnectionRefusedError(111, "Connection refused"),
+    ],
+    ids=["erreur_sqlalchemy", "erreur_reseau_asyncpg"],
+)
+async def test_readiness_returns_503_when_database_is_unreachable(
+    app: FastAPI, client: AsyncClient, failure: Exception
+) -> None:
+    class UnreachableSession:
+        async def execute(self, *_: object, **__: object) -> None:
+            raise failure
+
+    async def override() -> AsyncIterator[UnreachableSession]:
+        yield UnreachableSession()
+
+    app.dependency_overrides[get_session] = override
+
+    response = await client.get("/api/v1/health/ready")
+
+    assert response.status_code == 503
+    assert response.json()["detail"] == "Base de donnees injoignable"
+
+
+@pytest.mark.parametrize("path", ["/openapi.json", "/metrics"])
+async def test_technical_endpoints_are_served(client: AsyncClient, path: str) -> None:
+    assert (await client.get(path)).status_code == 200

apps/backend/tests/conftest.py

@@ -0,0 +1,32 @@
+import os
+from collections.abc import AsyncIterator, Iterator
+
+import pytest
+from fastapi import FastAPI
+from httpx import ASGITransport, AsyncClient
+
+from app.core.config import get_settings
+from app.main import create_app
+
+
+@pytest.fixture(autouse=True, scope="session")
+def environment() -> Iterator[None]:
+    os.environ.setdefault("APP_SECRET_KEY", "secret-de-test")
+    os.environ.setdefault(
+        "DATABASE_URL", "postgresql+asyncpg://enervision:enervision@localhost:5432/enervision_test"
+    )
+    get_settings.cache_clear()
+    yield
+    get_settings.cache_clear()
+
+
+@pytest.fixture
+def app() -> FastAPI:
+    return create_app()
+
+
+@pytest.fixture
+async def client(app: FastAPI) -> AsyncIterator[AsyncClient]:
+    transport = ASGITransport(app=app)
+    async with AsyncClient(transport=transport, base_url="http://test") as async_client:
+        yield async_client