Replace 3-tab navigation with a single monitoring dashboard.
- Replace tab bar with minimal status line (pulse + counts + version)
- Maintenance becomes a toggleable left sidebar (m key)
- Compact list: active (●) and scheduled (○) windows
- Enter opens full-screen detail with end/delete actions
- Settings becomes a centered floating overlay (S key)
- Alerts/Nodes/Users sub-sections with left/right navigation
- Full CRUD support inside overlay with returnState tracking
- Remove currentTab, switchTab, tab constants, tab click zones
- Replace deleteTab with deleteKind string for cleaner dispatch
- Separate settingsCursor/settingsOffset from main cursor
- Panel focus: maint → monitors → logs → detail
- Context-sensitive footer key hints per focused panel
