feat: toggle between picker and grid without closing panes

Add pause()/resume() to DirectGridRenderer that detach/reattach frame
listeners without killing captures or PTY sessions. switchToPicker now
pauses the grid, switchToGrid resumes it. Panes keep running in the
background while browsing the project list.

Footer shows "t grid" hint when panes are active in the background.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/direct-grid.ts

@@ -89,6 +89,31 @@ export class DirectGridRenderer {
     this.writeRaw(SHOW_CURSOR)
   }
 
+  pause() {
+    this.running = false
+    if (this.titleTimer) { clearInterval(this.titleTimer); this.titleTimer = null }
+    // Detach frame listeners (stops rendering) but keep captures alive
+    for (const p of this.panes) p.directPane.detach()
+  }
+
+  resume() {
+    this.running = true
+    this.writeRaw(HIDE_CURSOR + CLEAR)
+    // Reattach frame listeners and redraw
+    for (let i = 0; i < this.panes.length; i++) {
+      const p = this.panes[i]
+      const dp = p.directPane
+      const idx = i
+      dp.attach(p.session.name)
+      dp.onFrame = (lines) => {
+        if (!this.running) return
+        this.drawPane(idx, lines)
+      }
+    }
+    this.repositionAll()
+    this.titleTimer = setInterval(() => this.refreshTitles(), 1000)
+  }
+
   // ─── Getters ───────────────────────────────────────────
 
   get focusIndex() { return this._focusIndex }