fix(memos-local-plugin): guard OpenClaw runtime startup

[hijzy]

Summary

• add an OpenClaw runtime lock to block duplicate plugin instances before tools/hooks register
• fail startup on viewer port conflicts and clean up partial runtime state
• keep lightweight local memories searchable/listable without an LLM final filter, while preserving full-mode self-evolution boundaries
• cover runtime locking, duplicate startup, lightweight retrieval, delayed agent_end recovery, and partial migration behavior

Tests

• npm test -- --run tests/unit
• npm run lint
• npm run build
• git diff --check --cached