feat: initial implementation of @astrojs/discovery integration

This commit introduces a comprehensive Astro integration that automatically
generates discovery files for websites:

Features:
- robots.txt with LLM bot support (Anthropic-AI, GPTBot, etc.)
- llms.txt for AI assistant context and instructions
- humans.txt for team credits and site information
- Automatic sitemap integration via @astrojs/sitemap

Technical Details:
- TypeScript implementation with full type safety
- Configurable HTTP caching headers
- Custom template support for all generated files
- Sensible defaults with extensive customization options
- Date-based versioning (2025.11.03)

Testing:
- 34 unit tests covering all generators
- Test coverage for robots.txt, llms.txt, and humans.txt
- Integration with Vitest

Documentation:
- Comprehensive README with examples
- API reference documentation
- Contributing guidelines
- Example configurations (minimal and full)

CHANGELOG.md

@@ -0,0 +1,81 @@
+# Changelog
+
+All notable changes to @astrojs/discovery will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project uses date-based versioning (YYYY.MM.DD).
+
+## [2025.11.03] - 2025-11-03
+
+### Added
+- Initial release of @astrojs/discovery
+- Automatic robots.txt generation with LLM bot support
+- Automatic llms.txt generation for AI assistant context
+- Automatic humans.txt generation for team credits
+- Integration with @astrojs/sitemap for sitemap-index.xml
+- Configurable HTTP caching headers
+- Custom template support for all generated files
+- TypeScript type definitions
+- Comprehensive configuration options
+- Example configurations (minimal and full)
+
+### Features
+- **robots.txt**
+  - Default allow-all policy
+  - LLM-specific bot rules (Anthropic-AI, GPTBot, etc.)
+  - Custom agent configurations
+  - Crawl delay settings
+  - Custom rules support
+
+- **llms.txt**
+  - Site description and key features
+  - Important pages listing
+  - AI assistant instructions
+  - API endpoint documentation
+  - Technology stack information
+  - Brand voice guidelines
+  - Custom sections
+
+- **humans.txt**
+  - Team member information
+  - Thanks/credits section
+  - Site technical information
+  - Project story
+  - Fun facts
+  - Development philosophy
+  - Custom sections
+
+- **Configuration**
+  - Sensible defaults
+  - Full customization options
+  - Environment-based toggles
+  - Dynamic content support
+  - Cache control configuration
+
+### Documentation
+- Comprehensive README with examples
+- API reference documentation
+- Contributing guidelines
+- Example configurations
+- Integration guides
+
+## Future Enhancements
+
+### Planned Features
+- security.txt support (RFC 9116)
+- ads.txt support for advertising
+- manifest.json for PWA
+- RSS feed integration
+- OpenGraph tags injection
+- Structured data (JSON-LD)
+- Analytics discovery
+- i18n support for multi-language sites
+
+### Testing
+- Unit tests for generators
+- Integration tests
+- E2E tests with real Astro projects
+
+---
+
+For more information, see [README.md](README.md)