* fix(memory): find_by_entity returns all matches by default (limit=None, not 10)
* Address review: move find_by_entity tests to the AgentMemory area
The regression tests lived in tests/test_seed_manager.py, mixing unrelated
domains. Moved to tests/context/test_agent_memory_find_by_entity.py with a
shared fixture; the unbounded default itself is unchanged and deliberate —
it IS the fix (#1018): an erasure workflow computing what references an
entity cannot paginate, so silently truncating at 10 left live references
behind. Callers that want a page pass an explicit limit.
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Co-authored-by: Sameer Kadam <sskadam6305@gmail.com>