docs: add comprehensive CHANGELOG.md with version history

CHANGELOG.md

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+# Changelog
+
+All notable changes to the **Antigravity Awesome Skills** collection are documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+---
+
+## [1.0.0] - 2026-01-19 - "Marketing Edition"
+
+### Added
+
+- **23 Marketing & Growth skills** from [coreyhaines31/marketingskills](https://github.com/coreyhaines31/marketingskills):
+  - **CRO**: `page-cro`, `signup-flow-cro`, `onboarding-cro`, `form-cro`, `popup-cro`, `paywall-upgrade-cro`
+  - **Content**: `copywriting`, `copy-editing`, `email-sequence`
+  - **SEO**: `seo-audit`, `programmatic-seo`, `schema-markup`, `competitor-alternatives`
+  - **Paid**: `paid-ads`, `social-content`
+  - **Growth**: `referral-program`, `launch-strategy`, `free-tool-strategy`
+  - **Analytics**: `ab-test-setup`, `analytics-tracking`
+  - **Strategy**: `pricing-strategy`, `marketing-ideas`, `marketing-psychology`
+- New "Marketing & Growth" category in Features table
+
+### Changed
+
+- Total skills count: **179**
+
+---
+
+## [0.7.0] - 2026-01-19 - "Education Edition"
+
+### Added
+
+- **Moodle External API Development** skill via PR #6
+- Comprehensive Moodle LMS web service API development
+
+### Changed
+
+- Total skills count: **156**
+
+---
+
+## [0.6.0] - 2026-01-19 - "Vibeship Integration"
+
+### Added
+
+- **57 skills** from [vibeforge1111/vibeship-spawner-skills](https://github.com/vibeforge1111/vibeship-spawner-skills):
+  - AI Agents category (~30 skills)
+  - Integrations & APIs (~25 skills)
+  - Maker Tools (~11 skills)
+- Alphabetically sorted skill registry
+
+### Changed
+
+- Total skills count: **155**
+
+---
+
+## [0.5.0] - 2026-01-18 - "Agent Manager"
+
+### Added
+
+- **Agent Manager Skill** - Multi-agent orchestration via tmux
+- Major repository expansion with community contributions
+
+### Changed
+
+- Total skills count: **131**
+
+---
+
+## [0.4.0] - 2026-01-18 - "Security Fortress"
+
+### Added
+
+- **60+ Cybersecurity skills** from [zebbern/claude-code-guide](https://github.com/zebbern/claude-code-guide):
+  - Ethical Hacking Methodology
+  - Metasploit Framework
+  - Burp Suite Testing
+  - SQLMap, Active Directory, AWS Pentesting
+  - OWASP Top 100 Vulnerabilities
+  - Red Team Tools
+- `claude-code-guide` skill
+
+### Changed
+
+- Total skills count: ~90
+
+---
+
+## [0.3.0] - 2026-01-17 - "First Stable Registry"
+
+### Added
+
+- Complete skill registry table in README
+- GitHub workflow automation
+- SEO optimizations
+
+### Changed
+
+- Total skills count: **71**
+
+---
+
+## [0.2.0] - 2026-01-16 - "Official Skills"
+
+### Added
+
+- **Official Anthropic skills** integration
+- **Vercel Labs skills** integration
+- BlockRun: Agent Wallet for LLM Micropayments
+- 7 new skills from GitHub analysis
+
+### Changed
+
+- Total skills count: ~65
+
+---
+
+## [0.1.0] - 2026-01-15 - "Initial Release"
+
+### Added
+
+- **58 core skills** aggregated from community:
+  - [obra/superpowers](https://github.com/obra/superpowers) - Original Superpowers
+  - [guanyang/antigravity-skills](https://github.com/guanyang/antigravity-skills) - Core extensions
+  - [diet103/claude-code-infrastructure-showcase](https://github.com/diet103/claude-code-infrastructure-showcase) - Infrastructure skills
+  - [ChrisWiles/claude-code-showcase](https://github.com/ChrisWiles/claude-code-showcase) - React UI patterns
+  - [travisvn/awesome-claude-skills](https://github.com/travisvn/awesome-claude-skills) - Loki Mode
+  - [alirezarezvani/claude-skills](https://github.com/alirezarezvani/claude-skills) - Senior Engineering
+- Universal **SKILL.md** format
+- Compatibility with Claude Code, Gemini CLI, Cursor, Copilot, Antigravity
+
+---
+
+## Credits
+
+See [README.md](README.md#credits--sources) for full attribution.
+
+## License
+
+MIT License - See [LICENSE](LICENSE) for details.