feat: add retrieval observation log

[cafitac]

Summary

• add a secret-safe local retrieval observation log for Priority 5 dogfood/noise monitoring
• add agent-memory retrieve --observe <surface> and agent-memory observations list <db>
• have Hermes pre-LLM hook automatically record local observations without storing raw query text
• document observation review in README and Hermes dogfood docs

Test Plan

• uv run pytest tests/test_cli.py::test_python_module_cli_retrieve_observe_records_secret_safe_local_observation tests/test_cli.py::test_python_module_cli_hermes_pre_llm_hook_outputs_context_for_hermes_shell_hook_payload -q -> 2 passed
• uv run pytest tests/test_cli.py tests/test_retrieval_evaluation.py -q -> 83 passed
• real CLI smoke: agent-memory retrieve --observe cli-smoke + agent-memory observations list redaction check -> ok
• real Hermes hook smoke: agent-memory hermes-pre-llm-hook + agent-memory observations list -> ok
• uv run pytest tests/ -q -> 167 passed
• uv run python scripts/check_release_metadata.py -> ok
• uv run python scripts/smoke_release_readiness.py -> ok
• npm pack --dry-run -> ok
• git diff --check -> ok
• node --check bin/agent-memory.js -> ok
• static diff secret scan -> finding_count: 0