fix(zapier): harden null-body handling and error messages

From an independent review pass:
- Guard search / get / add against a null or empty 2xx body (previously an
  uncaught TypeError on .results / .status); return [] or an empty object.
- Stringify non-string API error detail so a thrown message never renders as
  "[object Object]".
- Correct the Add sample to the default no-wait shape {event_id, status}.
- Add a regression unit test for the null-body path.

Verified: build + zapier validate + 16 tests (13 unit, 3 live E2E), plus a
live check of the v3-add to /v1/event poll cross-version path.

integrations/zapier-mem0/test/unit.test.ts

@@ -124,6 +124,18 @@ describe('search / get array-shape enforcement (offline)', () => {
 		} as any);
 		expect(z.requests[0].params).toEqual({ page: 2, page_size: 10 });
 	});
+
+	it('search and get_memories return [] on a null/empty body (no crash)', async () => {
+		const zSearch = makeZ([{ data: null }]);
+		const found = await searchMemories.operation.perform(zSearch, {
+			inputData: { query: 'x', user_id: 'u1' },
+		} as any);
+		expect(found).toEqual([]);
+
+		const zGet = makeZ([{ data: null }]);
+		const all = await getMemories.operation.perform(zGet, { inputData: { user_id: 'u1' } } as any);
+		expect(all).toEqual([]);
+	});
 });
 
 describe('delete_memory (offline)', () => {