fix: preserve collection_name on MCP search retry

[trek-e]

What does this PR do?

Fixes transient-retry behavior in mempalace_search so the retry call preserves collection_name.

• Root cause: tool_search passed collection_name on the initial search_memories(...) call but dropped it on retry.
• Fix: pass _config.collection_name on the retry call as well.
• Adds regression test test_search_retry_preserves_collection_name to ensure both attempts use the same configured collection.

Closes #1623.

How to test

1. Run focused regression slice:
   • uv run pytest tests/test_mcp_server.py -k "search_retries_once_on_hnsw_flush_transient or search_retry_preserves_collection_name or search_with_wing_filter or search_with_room_filter" -q
2. Verify retry uses configured collection through the new test.

Validation run for this PR:

• uv run ruff check . -> pass
• Focused pytest slice above -> pass (4 passed)
• Full suite command from contributing docs:
  • uv run pytest tests/ -v --ignore=tests/benchmarks
  • Current branch shows 4 unrelated existing failures in tests/test_cli.py, tests/test_repair.py, and tests/test_searcher.py.

Checklist

• Tests pass (python -m pytest tests/ -v)
• No hardcoded paths
• Linter passes (ruff check .)

[gemini-code-assist]

Code Review

This pull request ensures that the configured collection name is preserved and passed during search retries in tool_search. It also adds a unit test to verify this behavior. There are no review comments, so I have no feedback to provide.