fix(tui): use panel width for table layout in split-pane mode

Table columns were computed from terminal width, causing row wrapping
when the monitors panel only gets 70% of the space. Introduced
contentWidth field set per-tab in viewDashboard. computeLayout,
isWide, and renderTable now use contentWidth for column visibility,
available space, and max table width calculations.

Columns gracefully hide (SSL, RETRIES, TYPE, UPTIME) when the panel
is narrower, matching the existing responsive breakpoint behavior.

internal/tui/view_dashboard.go

@@ -152,21 +152,26 @@ func (m Model) viewDashboard() string {
 	var content string
 	switch m.currentTab {
 	case tabMonitors:
-		monitors := m.viewSitesTab()
-		if m.termWidth >= wideBreakpoint {
+		showSidebar := m.termWidth >= wideBreakpoint
+		if showSidebar {
 			availW := m.termWidth - chromePadH
 			leftW := availW * 70 / 100
 			rightW := availW - leftW
+			m.contentWidth = leftW
+			monitors := m.viewSitesTab()
 			left := lipgloss.NewStyle().Width(leftW).Render(monitors)
 			sidebar := m.viewLogsSidebar(rightW)
 			right := lipgloss.NewStyle().Width(rightW).Render(sidebar)
 			content = lipgloss.JoinHorizontal(lipgloss.Top, left, right)
 		} else {
-			content = monitors
+			m.contentWidth = m.termWidth
+			content = m.viewSitesTab()
 		}
 	case tabMaint:
+		m.contentWidth = m.termWidth
 		content = m.viewMaintTab()
 	case tabSettings:
+		m.contentWidth = m.termWidth
 		content = m.viewSettingsTab()
 	}