feat: merge cartsnitch/api into api/ subdirectory

Consolidate API gateway service into monorepo.
Squashed from https://github.com/cartsnitch/api main (89bacb1).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/cartsnitch_api/routes/alerts.py

@@ -0,0 +1,44 @@
+"""Alert routes: list alerts, manage settings."""
+
+from uuid import UUID
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from cartsnitch_api.auth.dependencies import get_current_user
+from cartsnitch_api.database import get_db
+from cartsnitch_api.schemas import AlertResponse, AlertSettingsRequest, AlertSettingsResponse
+from cartsnitch_api.services.alerts import AlertService
+
+router = APIRouter(prefix="/alerts", tags=["alerts"])
+
+
+@router.get("", response_model=list[AlertResponse])
+async def list_alerts(
+    user_id: UUID = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    svc = AlertService(db)
+    return await svc.list_alerts(user_id)
+
+
+@router.get("/settings", response_model=AlertSettingsResponse)
+async def get_alert_settings(
+    user_id: UUID = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    svc = AlertService(db)
+    return await svc.get_settings(user_id)
+
+
+@router.put("/settings")
+async def update_alert_settings(
+    body: AlertSettingsRequest,
+    user_id: UUID = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    raise HTTPException(
+        status_code=status.HTTP_501_NOT_IMPLEMENTED,
+        detail="Alert settings persistence not yet implemented. "
+        "Use GET /alerts/settings for current defaults.",
+    )