fix: correct Qdrant point ID type in dimension mismatch E2E test

Why this change is needed:
The test was failing not due to dimension mismatch logic, but because
of invalid point ID format. Qdrant requires point IDs to be either
unsigned integers or UUIDs.

How it solves it:
Changed from id=str(i) (which produces "0", "1", "2" - invalid) to
id=i (which produces 0, 1, 2 - valid unsigned integers).

Impact:
- Fixes false test failure caused by test code bug
- Now test will properly verify actual dimension mismatch handling
- Aligned with other E2E tests that use integer IDs

Testing:
Will verify on CI that test now runs to completion and checks real
dimension mismatch behavior (not test setup errors)

tests/test_e2e_multi_instance.py

@@ -1270,7 +1270,7 @@ async def test_dimension_mismatch_qdrant(
         for i in range(3):
             points.append(
                 models.PointStruct(
-                    id=str(i),
+                    id=i,  # Use integer ID instead of string
                     vector=[0.1] * 768,  # OLD dimension
                     payload={"content": f"Legacy content {i}", "id": f"doc_{i}"},
                 )