feat(tui): show session workspace (cwd) in the status bar

SessionWorkspaceBoundEvent already recorded the bound workspace root but
it was never surfaced. Map it to a new session.workspace_bound frame
(sealed ServerMessage variant, auto-registered; re-emitted on reconnect
via the snapshot replay), carry it on Session.WorkspaceRoot, and show it
home-abbreviated in the status bar (⌂ ~/Programs/correx). Golden test
pins the decode.

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

@@ -1,6 +1,7 @@
 package app
 
 import (
+	"os"
 	"strings"
 
 	"github.com/charmbracelet/lipgloss"
@@ -74,6 +75,9 @@ func (m Model) renderStatus() string {
 		if s.Status != "" {
 			parts = append(parts, lipgloss.NewStyle().Foreground(statusColor(t, s.Status)).Background(bg).Render(statusLabel(s.Status)))
 		}
+		if s.WorkspaceRoot != "" {
+			parts = append(parts, span("⌂ "+shortPath(s.WorkspaceRoot), t.P.Faint))
+		}
 	}
 
 	model := m.currentModel
@@ -391,6 +395,14 @@ func (m Model) eventRows(w, h int) []string {
 
 // --- width helpers ---
 
+// shortPath abbreviates the user's home dir to ~ for a compact cwd in the status bar.
+func shortPath(p string) string {
+	if home := os.Getenv("HOME"); home != "" && strings.HasPrefix(p, home) {
+		return "~" + p[len(home):]
+	}
+	return p
+}
+
 // fill left-justifies a styled line and pads with bg to width w.
 func (m Model) fill(s string, w int, bg lipgloss.Color) string {
 	return " " + padTo(s, w-1, bg)