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/coupons.py

@@ -0,0 +1,32 @@
+"""Coupon routes: browse, relevant matches."""
+
+from uuid import UUID
+
+from fastapi import APIRouter, Depends, Query
+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 CouponResponse
+from cartsnitch_api.services.coupons import CouponService
+
+router = APIRouter(prefix="/coupons", tags=["coupons"])
+
+
+@router.get("", response_model=list[CouponResponse])
+async def list_coupons(
+    store_id: UUID | None = Query(None),
+    user_id: UUID = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    svc = CouponService(db)
+    return await svc.list_coupons(store_id)
+
+
+@router.get("/relevant", response_model=list[CouponResponse])
+async def relevant_coupons(
+    user_id: UUID = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    svc = CouponService(db)
+    return await svc.relevant_coupons(user_id)