feat: vue détail d'un site (#51)

Ajoute la page de détail d'un site (fiche, mesure instantanée, jauge de
consommation, historique) en remplacement du placeholder. Les champs
null sont affichés explicitement avec leur raison plutôt que masqués.

Ajoute l'endpoint GET /sites/{id}/current côté backend, qui retourne la
dernière mesure connue d'un site sans filtre temporel, conformément au
contrat de l'issue.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012i5NteMLRZgfTAKB5GD37X

apps/backend/tests/api/test_sites.py

@@ -1,14 +1,15 @@
 from collections.abc import Callable, Iterator
+from datetime import UTC, datetime
 from uuid import uuid4
 
 import pytest
 from fastapi import FastAPI
 from httpx import AsyncClient
 
-from app.api.deps import get_current_principal, get_site_service
+from app.api.deps import get_current_principal, get_reading_service, get_site_service
 from app.core.principal import Principal
 from app.core.roles import AccountKind, Role
-from app.models.energy import Site
+from app.models.energy import Reading, Site
 from app.services.site import SiteNotFoundError
 
 
@@ -47,6 +48,26 @@ class FauxService:
         return self.site
 
 
+def reading(site_id: str = "site-1") -> Reading:
+    return Reading(
+        reading_id=1,
+        site_id=site_id,
+        timestamp=datetime(2026, 9, 16, tzinfo=UTC),
+        source="csv",
+        consumption_kw=42.5,
+        data_quality="good",
+        raw_data={},
+    )
+
+
+class FauxReadingService:
+    def __init__(self, derniere: Reading | None) -> None:
+        self._derniere = derniere
+
+    async def get_latest(self, site_id: str) -> Reading | None:
+        return self._derniere
+
+
 @pytest.fixture
 def lecteur_connecte(app: FastAPI) -> Iterator[None]:
     app.dependency_overrides[get_current_principal] = lambda: principal()
@@ -67,6 +88,19 @@ def servi(
     app.dependency_overrides.pop(get_site_service, None)
 
 
+@pytest.fixture
+def readings_servis(
+    app: FastAPI, lecteur_connecte: None
+) -> Iterator[Callable[[Reading | None], FauxReadingService]]:
+    def installe(derniere: Reading | None) -> FauxReadingService:
+        service = FauxReadingService(derniere)
+        app.dependency_overrides[get_reading_service] = lambda: service
+        return service
+
+    yield installe
+    app.dependency_overrides.pop(get_reading_service, None)
+
+
 async def test_list_sites_returns_the_sites(
     servi: Callable[..., FauxService], client: AsyncClient
 ) -> None:
@@ -139,3 +173,45 @@ async def test_get_site_returns_404_when_the_session_finds_nothing(
     response = await client.get("/api/v1/sites/inconnu")
 
     assert response.status_code == 404
+
+
+async def test_get_current_returns_the_latest_reading_regardless_of_its_age(
+    servi: Callable[..., FauxService],
+    readings_servis: Callable[[Reading | None], FauxReadingService],
+    client: AsyncClient,
+) -> None:
+    servi()
+    readings_servis(reading())
+
+    response = await client.get("/api/v1/sites/site-1/current")
+
+    assert response.status_code == 200
+    corps = response.json()
+    assert corps["consumption_kw"] == 42.5
+
+
+async def test_get_current_returns_null_when_the_site_has_no_reading(
+    servi: Callable[..., FauxService],
+    readings_servis: Callable[[Reading | None], FauxReadingService],
+    client: AsyncClient,
+) -> None:
+    servi()
+    readings_servis(None)
+
+    response = await client.get("/api/v1/sites/site-1/current")
+
+    assert response.status_code == 200
+    assert response.json() is None
+
+
+async def test_get_current_returns_404_for_an_unknown_site(
+    servi: Callable[..., FauxService],
+    readings_servis: Callable[[Reading | None], FauxReadingService],
+    client: AsyncClient,
+) -> None:
+    servi(SiteNotFoundError("site-inconnu"))
+    readings_servis(None)
+
+    response = await client.get("/api/v1/sites/site-inconnu/current")
+
+    assert response.status_code == 404