M6-T09: add Energy data API (prices/costs/summary/dsmr-latest/recompute/tibber-test)

- routes/api/energy.py + schemas/energy.py: GET prices (tibber points or manual
  tariff, buy/sell consistent with the pricing strategies), GET costs (time
  window + limit, ascending), GET costs/summary (summarize passthrough), GET
  dsmr/latest, POST costs/recompute (idempotent, <=366d guard, CSRF), POST
  tibber/test (three-state, token never echoed, CSRF).
- main.py registers router; OpenAPI re-exported; tests for all endpoints.

app/main.py

@@ -13,6 +13,7 @@ from sqlalchemy.orm import Session
 from app import models  # noqa: F401
 from app.api.routes.api.config import router as api_config_router
 from app.api.routes.api.data import router as api_data_router
+from app.api.routes.api.energy import router as api_energy_router
 from app.api.routes.api.energy_contracts import router as api_energy_contracts_router
 from app.api.routes.api.expose import router as api_expose_router
 from app.api.routes.api.modbus import router as api_modbus_router
@@ -288,6 +289,7 @@ def create_app() -> FastAPI:
     app.include_router(status.router)
     app.include_router(api_config_router)
     app.include_router(api_data_router)
+    app.include_router(api_energy_router)
     app.include_router(api_energy_contracts_router)
     app.include_router(api_expose_router)
     app.include_router(api_modbus_router)