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/services/receiptwitness.py

@@ -0,0 +1,33 @@
+"""HTTP client for ReceiptWitness internal API."""
+
+from typing import Any, cast
+
+import httpx
+
+from cartsnitch_api.config import settings
+
+
+class ReceiptWitnessClient:
+    def __init__(self) -> None:
+        self.base_url = settings.receiptwitness_url
+        self.headers = {"X-Service-Key": settings.service_key}
+
+    async def trigger_sync(self, user_id: str, store_slug: str) -> dict:
+        async with httpx.AsyncClient() as client:
+            resp = await client.post(
+                f"{self.base_url}/sync/{store_slug}",
+                headers=self.headers,
+                json={"user_id": user_id},
+            )
+            resp.raise_for_status()
+            return cast(dict[str, Any], resp.json())
+
+    async def get_sync_status(self, user_id: str) -> list[dict]:
+        async with httpx.AsyncClient() as client:
+            resp = await client.get(
+                f"{self.base_url}/sync/status",
+                headers=self.headers,
+                params={"user_id": user_id},
+            )
+            resp.raise_for_status()
+            return cast(list[dict[str, Any]], resp.json())