Summary

• bridge AIAgent._touch_activity() to a best-effort Kanban auto-heartbeat helper for dispatcher workers
• refresh both claim TTL and board heartbeat timestamps without persisting activity descriptions
• add focused regressions for worker heartbeat writes, rate limiting, stale-reclaim protection, and non-fatal failures

Testing

• uv run --frozen --with pytest python -m pytest -o addopts='' tests/run_agent/test_kanban_auto_heartbeat.py -q
• uv run --frozen --with pytest python -m pytest -o addopts='' tests/tools/test_kanban_tools.py -k 'heartbeat' -q
• uv run --frozen --with pytest python -m pytest -o addopts='' tests/hermes_cli/test_kanban_db.py -k 'detect_stale_skips_task_with_recent_heartbeat or heartbeat_extends_claim' -q
• uv run --frozen --with ruff ruff check run_agent.py tools/kanban_tools.py tests/run_agent/test_kanban_auto_heartbeat.py
• git diff --check origin/main...HEAD

Closes #31752.