docs: register /spec skill in README, AGENTS, CLAUDE.md project tree

Adds /spec to the three discoverability surfaces it was missing:
- README.md sprint skills table (between /autoplan and /learn)
- AGENTS.md plan-mode reviews table
- CLAUDE.md project structure tree (between /investigate and /retro)

/spec shipped in v1.47.0.0 with CHANGELOG coverage but the entry-point
docs hadn't been updated; a user landing on README or AGENTS would not
discover the skill exists without reading CHANGELOG.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

AGENTS.md

@@ -21,6 +21,7 @@ Invoke them by name (e.g., `/office-hours`).
 | `/plan-tune` | Self-tune AskUserQuestion sensitivity per question. |
 | `/autoplan` | One command runs CEO → design → eng → DX review. |
 | `/design-consultation` | Build a complete design system from scratch. |
+| `/spec` | Turn vague intent into a precise, executable spec in five phases. Files a GitHub issue, optionally spawns a Claude Code agent in a fresh worktree, and lets `/ship` close the source issue on merge. |
 
 ### Implementation + review
 

CLAUDE.md

@@ -111,6 +111,7 @@ gstack/
 ├── land-and-deploy/ # /land-and-deploy skill (merge → deploy → canary verify)
 ├── office-hours/    # /office-hours skill (YC Office Hours — startup diagnostic + builder brainstorm)
 ├── investigate/     # /investigate skill (systematic root-cause debugging)
+├── spec/            # /spec skill (five-phase spec → GitHub issue, optional agent spawn, /ship auto-closes)
 ├── retro/           # Retrospective skill (includes /retro global cross-project mode)
 ├── bin/             # CLI utilities (gstack-repo-mode, gstack-slug, gstack-config, etc.)
 ├── document-release/ # /document-release skill (post-ship doc updates + Diataxis coverage map)

README.md

@@ -204,6 +204,7 @@ Each skill feeds into the next. `/office-hours` writes a design doc that `/plan-
 | `/browse` | **QA Engineer** | Give the agent eyes. Real Chromium browser, real clicks, real screenshots. ~100ms per command. `/open-gstack-browser` launches GStack Browser with sidebar, anti-bot stealth, and auto model routing. |
 | `/setup-browser-cookies` | **Session Manager** | Import cookies from your real browser (Chrome, Arc, Brave, Edge) into the headless session. Test authenticated pages. |
 | `/autoplan` | **Review Pipeline** | One command, fully reviewed plan. Runs CEO → design → eng review automatically with encoded decision principles. Surfaces only taste decisions for your approval. |
+| `/spec` | **Spec Author** | Turn vague intent into a precise, executable spec in five phases (why, scope, technical with mandatory code-reading, draft, file). Codex quality gate before file (blocks below 7/10), fail-closed secret redaction, dedupe against existing issues, archive to `$GSTACK_STATE_ROOT/projects/$SLUG/specs/` for team-corpus recall. `--execute` spawns `claude -p` in a fresh worktree; `/ship` auto-closes the source issue on merge. Plan-mode aware. |
 | `/learn` | **Memory** | Manage what gstack learned across sessions. Review, search, prune, and export project-specific patterns, pitfalls, and preferences. Learnings compound across sessions so gstack gets smarter on your codebase over time. |
 
 ### Which review should I use?