Persist explicit memory feedback

[importcpp]

Summary

• persist explicit weight feedback through the store write path
• rebuild the search projection so later recall uses the updated weight
• verify persistence by reopening the store in the regression test

Problem

Store.feedback() returned an updated in-memory record, but neither the Markdown source of truth nor the SQLite search projection was updated. Reopening the store restored the old weight and recall ranking.

Testing

• uv run pytest -q --cov=agent_memory --cov-report=term-missing --cov-fail-under=85 (388 passed, 90.91% coverage)
• uv run ruff check .
• uv run mypy