feat(tui): pin detail panel footer keys at bottom of sidebar

Footer keys (period selector, edit/history/SLA shortcuts, Esc) are now
pinned at the bottom of the detail panel, always visible regardless of
scroll position. Scrollable content fills the space between the header
and the pinned footer.

internal/tui/view_dashboard.go

@@ -192,7 +192,8 @@ func (m Model) viewMonitorsLayout() string {
 		}
 		monHeight := lipgloss.Height(monPanel)
 		detail := m.viewDetailInline(detailW-2, monHeight)
-		detailPanel := m.zones.Mark("panel-detail", m.titledPanelH(title, detail, detailW, monHeight, m.detailScrollOffset, m.focusedPanel == panelDetail))
+		footer := m.detailFooter(detailW - 2)
+		detailPanel := m.zones.Mark("panel-detail", m.titledPanelH(title, detail, footer, detailW, monHeight, m.detailScrollOffset, m.focusedPanel == panelDetail))
 		topParts = append(topParts, detailPanel)
 	}