BUG: Memories routes define Pydantic response models (Memory, GenerateMemoriesResponse, ...) that are never used; responses are unvalidated and inconsistent with other routers ```

### Is there an existing issue for this?

- [x] I have searched the existing issues

### What happened?

`backend/app/routes/memories.py:39-112` defines `MemoryImage`, `Memory`, `GenerateMemoriesResponse`, `TimelineResponse`, `OnThisDayResponse`, `LocationCluster`, `LocationsResponse` — but none of the endpoints set `response_model=`, and they instead return raw `{"data": {...}, "success": ..., "message": ...}` dicts whose shape doesn't match those models. Result: dead code, no response validation, and an envelope inconsistent with every other router (which uses typed `response_model`s).

**Fix:** either wire the models in via `response_model=` (and align the `{data, success, message}` envelope), or delete the unused models.

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