feat(tui-go): show last-activity date in the starting-view session list

The idle "sessions" panel listed id/status/name/stage but no time at all. Add a
right-aligned last-activity timestamp (Session.LastEventAt) per row — "Jan 02
15:04" within the current year, "Jan 02 2006" for older — so old sessions are
distinguishable at a glance. The name is truncated first so the box's width
clamp never eats the date column. (The R resume overlay already shows a relative
age; this is the live list on the starting screen.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/tui-go/internal/app/view.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"time"
 
 	"github.com/charmbracelet/lipgloss"
 	"github.com/charmbracelet/x/ansi"
@@ -431,16 +432,46 @@ func (m Model) sessionRows(w int) []string {
 		idCell := t.span("["+short+"] ", t.P.Faint)
 		statusCell := lipgloss.NewStyle().Foreground(statusColor(t, s.Status)).Background(t.P.Bg).Bold(true).
 			Render(padRaw(statusLabel(s.Status), 9))
-		nameCell := lipgloss.NewStyle().Foreground(nameFg).Background(t.P.Bg).Render(" " + s.Name)
-		stage := ""
+		stageStr := ""
 		if s.CurrentStage != "" {
-			stage = t.span(" ["+s.CurrentStage+"]", t.P.Dim)
+			stageStr = " [" + s.CurrentStage + "]"
 		}
-		rows = append(rows, bar+idCell+statusCell+nameCell+stage)
+		dateCell := t.span(shortDateTime(s.LastEventAt), t.P.Faint)
+
+		// Right-align the last-activity date; truncate the name first so the date column
+		// always survives the box's width clamp (padTo) even on a slim panel.
+		fixed := lipgloss.Width(bar) + lipgloss.Width(idCell) + lipgloss.Width(statusCell) + 1 + len([]rune(stageStr))
+		name := s.Name
+		if budget := w - fixed - lipgloss.Width(dateCell) - 1; budget >= 1 && len([]rune(name)) > budget {
+			name = truncate(name, budget)
+		}
+		nameCell := lipgloss.NewStyle().Foreground(nameFg).Background(t.P.Bg).Render(" " + name)
+		stageCell := t.span(stageStr, t.P.Dim)
+
+		left := bar + idCell + statusCell + nameCell + stageCell
+		gap := w - lipgloss.Width(left) - lipgloss.Width(dateCell)
+		if gap < 1 {
+			gap = 1
+		}
+		rows = append(rows, left+t.span(strings.Repeat(" ", gap), t.P.Bg)+dateCell)
 	}
 	return rows
 }
 
+// shortDateTime formats a millis-since-epoch instant as a compact local timestamp for the
+// session list: "Jan 02 15:04" within the current year, "Jan 02 2006" for older years.
+// Empty for a zero/absent time (renders as no date rather than a bogus epoch).
+func shortDateTime(ms int64) string {
+	if ms <= 0 {
+		return ""
+	}
+	ts := time.UnixMilli(ms)
+	if ts.Year() != time.Now().Year() {
+		return ts.Format("Jan 02 2006")
+	}
+	return ts.Format("Jan 02 15:04")
+}
+
 func (m Model) workflowRows(w int) []string {
 	t := m.theme
 	if len(m.workflows) == 0 {