Add gstack skill documentation files

[sonakajima9]

This PR adds comprehensive documentation for the gstack skill system, a collection of specialized AI-assisted development workflows.

Summary

Added 28 markdown documentation files that define individual "skills" - specialized modes for different development tasks. Each skill includes metadata (name, version, tier, description), allowed tools, and detailed preamble setup code for initialization and telemetry.

Key Skills Added

Planning & Design Skills:

• office-hours.md - YC-style brainstorming for new ideas and product thinking
• design-consultation.md - Design system creation and brand guidelines
• design-shotgun.md - Multi-variant design exploration
• plan-ceo-review.md, plan-design-review.md, plan-eng-review.md - Planning phase reviews

Implementation Skills:

• design-html.md - Production HTML/CSS generation from designs
• design-review.md - Visual QA and design polish
• ship.md - PR creation and code shipping
• land-and-deploy.md - Merge, CI/CD, and production verification
• qa.md, qa-only.md - Quality assurance workflows
• review.md - Code review

Operational Skills:

• cso.md - Security audits and threat modeling
• investigate.md - Systematic debugging with root cause analysis
• health.md - Code quality dashboard
• benchmark.md - Performance regression detection
• canary.md - Post-deploy monitoring
• document-release.md - Post-ship documentation updates
• retro.md - Retrospectives

Utility Skills:

• browse.md, connect-chrome.md - Browser automation and testing
• learn.md - Project learnings management
• checkpoint.md - Session state saving and resumption
• codex.md - OpenAI Codex integration
• autoplan.md - Automated review pipeline
• gstack-root.md - Root gstack browser tool
• gstack-upgrade.md - Version upgrades
• careful.md, freeze.md, guard.md - Safety guardrails
• setup-browser-cookies.md, setup-deploy.md, unfreeze.md - Setup utilities

Implementation Details

Each skill file includes:

• YAML frontmatter with metadata (name, version, preamble-tier, description)
• Allowed tools specification (Bash, Read, Write, Edit, Glob, Grep, Agent, WebSearch, AskUserQuestion)
• Comprehensive bash preamble for session management, telemetry, learnings tracking, and environment setup
• Skill-specific workflow documentation and usage patterns

The preamble code is consistent across skills and handles:

• Update checking
• Session tracking and cleanup
• Proactive mode configuration
• Telemetry logging
• Repository mode detection
• Project learnings loading
• Timeline event recording

https://claude.ai/code/session_01QJ8jBXerbo5hptRLGepShQ