Fusionne dev dans feat/endpoint-alertes-predictives

Resout les conflits additifs entre les routes alerts, recommendations
et stats mergees sur dev (PR #79, PR #82) pendant le developpement de
cette branche : deps.py, router.py, openapi.py, openapi.json,
test_openapi.py et 20-backend.md conservent desormais les trois routes.

apps/backend/app/schemas/recommendation.py

@@ -0,0 +1,14 @@
+from datetime import datetime
+
+from pydantic import BaseModel, ConfigDict
+
+
+class RecommendationResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    recommendation_id: int
+    alert_id: int
+    action: str
+    explanation: str
+    rule_reference: str
+    created_at: datetime

apps/backend/app/schemas/stats.py

@@ -0,0 +1,26 @@
+from datetime import datetime
+from typing import Literal
+
+from pydantic import BaseModel, ConfigDict
+
+
+class SiteSummaryResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    site_id: str
+    site_name: str
+    current_consumption_kw: float | None
+    capacity_kw: float
+    load_percent: float | None
+    data_quality: Literal["good", "partial", "degraded", "critical"]
+
+
+class StatsSummaryResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    timestamp: datetime
+    total_sites: int
+    total_consumption_kw: float
+    total_capacity_kw: float
+    average_load_percent: float
+    sites: list[SiteSummaryResponse]