Tab bar: Monitors | Maint | Settings (was 6 tabs).
Settings tab merges Alerts, Nodes, Users as sub-sections with
left/right arrow navigation. Each section keeps its own cursor,
keybindings, and CRUD operations.
Monitors tab now shows a log sidebar at >= 120 cols (70/30 split).
Under 120 cols, monitors render full-width without logs.
- Introduced tab constants (tabMonitors, tabMaint, tabSettings)
- Introduced section constants (sectionAlerts, sectionNodes, sectionUsers)
- Removed stateLogs and stateUsers states
- All magic tab numbers replaced with named constants
