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/purchases.py

@@ -0,0 +1,49 @@
+"""Purchase routes: list, detail, stats."""
+
+from uuid import UUID
+
+from fastapi import APIRouter, Depends, HTTPException, Query, 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 PurchaseDetailResponse, PurchaseResponse, PurchaseStatsResponse
+from cartsnitch_api.services.purchases import PurchaseService
+
+router = APIRouter(prefix="/purchases", tags=["purchases"])
+
+
+@router.get("", response_model=list[PurchaseResponse])
+async def list_purchases(
+    user_id: UUID = Depends(get_current_user),
+    store_id: UUID | None = Query(None),
+    page: int = Query(1, ge=1),
+    page_size: int = Query(20, ge=1, le=100),
+    db: AsyncSession = Depends(get_db),
+):
+    svc = PurchaseService(db)
+    return await svc.list_purchases(user_id, store_id, page, page_size)
+
+
+@router.get("/stats", response_model=PurchaseStatsResponse)
+async def purchase_stats(
+    user_id: UUID = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    svc = PurchaseService(db)
+    return await svc.get_stats(user_id)
+
+
+@router.get("/{purchase_id}", response_model=PurchaseDetailResponse)
+async def get_purchase(
+    purchase_id: UUID,
+    user_id: UUID = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    svc = PurchaseService(db)
+    try:
+        return await svc.get_purchase(purchase_id, user_id)
+    except LookupError:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND, detail="Purchase not found"
+        ) from None