feat: add update check preamble to all 9 skills

Every skill now runs bin/gstack-update-check on invocation. If an upgrade
is available, reads gstack-upgrade/SKILL.md inline upgrade flow.

Also adds AskUserQuestion to 5 skills that lacked it (gstack root, browse,
qa, retro, setup-browser-cookies) and Bash to plan-eng-review.

Simplifies qa and setup-browser-cookies setup blocks (removes META parsing).

SKILL.md

@@ -10,11 +10,21 @@ description: |
 allowed-tools:
   - Bash
   - Read
+  - AskUserQuestion
 
 ---
 <!-- AUTO-GENERATED from SKILL.md.tmpl — do not edit directly -->
 <!-- Regenerate: bun run gen:skill-docs -->
 
+## Update Check (run first)
+
+```bash
+_UPD=$(~/.claude/skills/gstack/bin/gstack-update-check 2>/dev/null || .claude/skills/gstack/bin/gstack-update-check 2>/dev/null || true)
+[ -n "$_UPD" ] && echo "$_UPD"
+```
+
+If output shows `UPGRADE_AVAILABLE <old> <new>`: read `~/.claude/skills/gstack/gstack-upgrade/SKILL.md` and follow the "Inline upgrade flow" (AskUserQuestion → upgrade if yes, `touch ~/.gstack/last-update-check` if no). If `JUST_UPGRADED <from> <to>`: tell user "Running gstack v{to} (just updated!)" and continue.
+
 # gstack browse: QA Testing & Dogfooding
 
 Persistent headless Chromium. First call auto-starts (~3s), then ~100-200ms per command.
@@ -23,12 +33,9 @@ Auto-shuts down after 30 min idle. State persists between calls (cookies, tabs,
 ## SETUP (run this check BEFORE any browse command)
 
 ```bash
-BROWSE_OUTPUT=$(browse/bin/find-browse 2>/dev/null || ~/.claude/skills/gstack/browse/bin/find-browse 2>/dev/null)
-B=$(echo "$BROWSE_OUTPUT" | head -1)
-META=$(echo "$BROWSE_OUTPUT" | grep "^META:" || true)
+B=$(browse/bin/find-browse 2>/dev/null || ~/.claude/skills/gstack/browse/bin/find-browse 2>/dev/null)
 if [ -n "$B" ]; then
   echo "READY: $B"
-  [ -n "$META" ] && echo "$META"
 else
   echo "NEEDS_SETUP"
 fi
@@ -39,13 +46,6 @@ If `NEEDS_SETUP`:
 2. Run: `cd <SKILL_DIR> && ./setup`
 3. If `bun` is not installed: `curl -fsSL https://bun.sh/install | bash`
 
-If you see `META:UPDATE_AVAILABLE`:
-1. Parse the JSON payload to get `current`, `latest`, and `command`.
-2. Tell the user: "A gstack update is available (current: X, latest: Y). OK to update?"
-3. **STOP and wait for approval.**
-4. Run the command from the META payload.
-5. Re-run the setup check above to get the updated binary path.
-
 ## IMPORTANT
 
 - Use the compiled binary via Bash: `$B <command>`