fix(antigravity): a pending shell approval reads as working, plus a reattach test

Review round: the footer hint is drawn only at rest, so nothing arms the idle check while the Run this command list is up. The stock.ts comment, wiki, changeset and test now say a pending approval shows as working until answered, and the test pins busy during the confirmation. Adds the antigravity copy of the reattached-pane settle test, and updates the promptGlyph comment and the fixture header.

src/session.ts

@@ -4780,7 +4780,7 @@ export class Session extends EventEmitter {
           : this._mux.capturePaneText?.(this._muxSession.muxName),
       sendEnter: () => this._mux?.sendInput(this.id, '\r'),
       // ⚠ NO fallback glyph here, unlike the screen-reading probe elsewhere in this file.
-      // Only claude, codex, pi, opencode, omp and gemini declare a promptGlyph; the other modes would fall back
+      // Only claude, codex, pi, opencode, omp, gemini and antigravity declare a promptGlyph; the other modes would fall back
       // to claude's `❯`, which is ALSO starship's default shell prompt (and pure's, and
       // spaceship's, and p10k lean's). On a shell session the line `❯ npm run build` sits
       // on screen for as long as the command runs, promptStillInComposer() reads that as