- Expand heartbeat interval presets to enforce a 5-minute minimum and include extended 48h/72h/1w options
- Add custom heartbeat entry in AgentsView with typed minute input, save/cancel actions, and validation/clamp behavior
- Show the Custom option only when the current interval is a preset, while preserving explicit custom interval labels when needed
- Update dashboard tests and heartbeat utility tests to cover new preset boundaries, custom option behavior, and health staleness expectations
- Document the 5-minute minimum heartbeat clamp behavior in agents documentation
- Refresh AgentDetailView on agent:updated SSE events while preserving local unsaved config edits
- Resync heartbeat and budget form state from latest runtime config when agent data changes
- Centralize heartbeat interval defaults/formatting in shared utilities and reuse them in AgentsView selectors
- Add dashboard tests for default heartbeat hints, unset runtime fallback behavior, and custom interval options
