Add Agent Skills System to Chibi

[terraboops]

This commit introduces a comprehensive skills system that enhances the
existing tools infrastructure with metadata support, validation, and
CLI management commands.

Core Changes:

1. Enhanced Tools System (src/tools.rs):

   • Added SkillMetadata struct with version, author, dependencies, categories
   • Updated Tool struct to include metadata field
   • Implemented skill validation (validate_skill_schema)
   • Added dependency checking (check_skill_dependencies, validate_dependencies)
   • Added skill query functions (skills_by_category, search_skills)
   • Added skill info formatting (format_skill_info)
   • All changes are backward compatible - existing tools work unchanged

2. CLI Integration (src/cli.rs):

   • Added SkillsCommand enum with List, Info, Validate, Run subcommands
   • Extended Cli struct with skills_command field
   • Updated parser to handle "chibi skills" subcommands
   • Updated help text with skills management section

3. Main Command Handler (src/main.rs):

   • Implemented skills list command with optional category filtering
   • Implemented skills info command with detailed output
   • Implemented skills validate command with comprehensive checks
   • Implemented skills run command for manual skill execution
   • Skills commands run early in the command chain (no context needed)

4. Documentation:

   • Added "Skills System" section to README.md
   • Created comprehensive SKILL_AUTHORING.md guide covering:
     • Skill interface requirements
     • Metadata field descriptions and use cases
     • Environment variables reference
     • Complete examples (bash, python)
     • Hook integration patterns
     • Best practices and security considerations
     • Testing and troubleshooting guides

5. Example Skills (examples/tools/):

   • hello_skill: Basic greeting skill demonstrating metadata
   • fetch_url_skill: URL fetcher demonstrating categories and dependencies

Features:

• Skill metadata is optional - existing tools continue to work
• Dependency validation warns about missing requirements
• Category-based filtering for skill organization
• Comprehensive validation before skill installation
• Manual skill execution for testing
• Full backward compatibility maintained

Usage Examples:

chibi skills list # List all skills
chibi skills list --category network # Filter by category
chibi skills info read_file # Show detailed info
chibi skills validate ./new_skill.sh # Validate before installing
chibi skills run hello_skill '{"name": "Alice"}' # Manual execution

Technical Notes:

• No new dependencies added (uses existing serde, std)
• Follows existing error handling patterns (io::Error)
• Matches existing code style and conventions
• Compiles cleanly with cargo check

[terraboops]

Closing this to do inside chibi-plugins, I guess 😅