feat(tui): SLA and history as sidebar detail modes

SLA and History views now render inside the detail sidebar panel
instead of taking over the full screen. Press s/h to switch modes,
Esc to return to default detail view. Cursor movement resets to
default mode.

- Add detailMode state (detailDefault/detailSLA/detailHistory)
- SLA sidebar: period selector, uptime bars, daily breakdown
- History sidebar: sparkline density, transition list, stats
- Panel title shows "SLA · name" or "History · name" in sub-modes
- Period keys [1]-[4] work in SLA mode from dashboard state

internal/tui/tui.go

@@ -97,6 +97,12 @@ const (
 	panelMaint    = 3
 )
 
+const (
+	detailDefault = 0
+	detailSLA     = 1
+	detailHistory = 2
+)
+
 const (
 	sortStatus  = 0
 	sortName    = 1
@@ -138,6 +144,7 @@ type Model struct {
 	termHeight      int
 	contentWidth    int
 	focusedPanel    int
+	detailMode      int
 	logScrollOffset int
 	editID          int
 	editToken       string