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_detail_inline.go

@@ -143,8 +143,6 @@ func (m Model) viewDetailSidebar(site models.Site, hist monitor.SiteHistory, wid
 		b.WriteString("  " + label.Render("No state changes") + "\n")
 	}
 
-	b.WriteString("\n  " + m.detailKeys() + "\n")
-
 	return lipgloss.NewStyle().Width(width).MaxWidth(width).Render(b.String())
 }
 
@@ -216,6 +214,33 @@ func (m Model) detailKeys() string {
 	return m.st.subtleStyle.Render("[e] Edit  [h] History  [s] SLA  [Esc] Back")
 }
 
+func (m Model) detailFooter(width int) string {
+	label := m.st.subtleStyle
+	var lines []string
+
+	switch m.detailMode {
+	case detailSLA:
+		var keys []string
+		for i, p := range slaPeriods {
+			k := fmt.Sprintf("[%s] %s", p.key, p.label)
+			if i == m.slaPeriodIdx {
+				keys = append(keys, m.st.titleStyle.Render(k))
+			} else {
+				keys = append(keys, label.Render(k))
+			}
+		}
+		lines = append(lines, "  "+strings.Join(keys, " "))
+		lines = append(lines, "  "+label.Render("[Esc] Back"))
+	case detailHistory:
+		lines = append(lines, "  "+label.Render("[Esc] Back"))
+	default:
+		lines = append(lines, "  "+m.detailKeys())
+	}
+
+	content := strings.Join(lines, "\n")
+	return lipgloss.NewStyle().Width(width).MaxWidth(width).Render(content)
+}
+
 func (m Model) fmtStatusWord(status string) string {
 	switch status {
 	case "DOWN", "SSL EXP":
@@ -292,20 +317,6 @@ func (m Model) viewSLASidebar(width, _ int) string {
 		}
 	}
 
-	b.WriteString("\n")
-
-	var keys []string
-	for i, p := range slaPeriods {
-		k := fmt.Sprintf("[%s] %s", p.key, p.label)
-		if i == m.slaPeriodIdx {
-			keys = append(keys, m.st.titleStyle.Render(k))
-		} else {
-			keys = append(keys, label.Render(k))
-		}
-	}
-	b.WriteString("  " + strings.Join(keys, " ") + "\n")
-	b.WriteString("  " + label.Render("[Esc] Back") + "\n")
-
 	return lipgloss.NewStyle().Width(width).MaxWidth(width).Render(b.String())
 }
 
@@ -368,7 +379,6 @@ func (m Model) viewHistorySidebar(width, _ int) string {
 		statParts = append(statParts, "avg "+fmtDuration(avg))
 	}
 	b.WriteString("  " + label.Render(strings.Join(statParts, " │ ")) + "\n")
-	b.WriteString("  " + label.Render("[Esc] Back") + "\n")
 
 	return lipgloss.NewStyle().Width(width).MaxWidth(width).Render(b.String())
 }