feat(billing): add GET /billing/state aggregating subscription + plan + features

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/api/endpoints/billing.py

@@ -9,7 +9,11 @@ from app.core.admin_database import get_admin_db
 from app.core.config import settings
 from app.models.account import Account
 from app.models.user import User
-from app.schemas.billing import CheckoutSessionCreate, CheckoutSessionResponse
+from app.schemas.billing import (
+    BillingStateResponse,
+    CheckoutSessionCreate,
+    CheckoutSessionResponse,
+)
 from app.services.billing import BillingService
 
 router = APIRouter(prefix="/billing", tags=["billing"])
@@ -34,3 +38,15 @@ async def create_checkout_session(
         cancel_url=f"{settings.FRONTEND_URL}/account/billing/select-plan",
     )
     return CheckoutSessionResponse(url=url)
+
+
+@router.get("/state", response_model=BillingStateResponse)
+async def get_billing_state(
+    current_user: Annotated[User, Depends(get_current_active_user)],
+    db: Annotated[AsyncSession, Depends(get_admin_db)],
+) -> BillingStateResponse:
+    account = (await db.execute(
+        select(Account).where(Account.id == current_user.account_id)
+    )).scalar_one()
+    state = await BillingService.get_billing_state(db, account)
+    return BillingStateResponse(**state)