Self-Documentation — Framework contribution guide and authoring docs

[striderZA]

Summary

Create documentation that makes the framework itself maintainable: contribution guide, authoring guides for agents/skills/rules, and improved AGENTS.md.

Scope

Framework Contribution Guide (docs/CONTRIBUTING.md)

• How to propose and add a new agent
• How to propose and add a new skill
• How to modify rules
• How to add a plugin
• PR requirements and review process
• Testing requirements

Agent Authoring Guide (docs/authoring-agents.md)

• Agent template with required sections
• Naming conventions
• Collaboration protocol patterns
• Output format standards
• Testing agents

Skill Authoring Guide (docs/authoring-skills.md)

• SKILL.md template with required sections
• Tool integration patterns
• Skill → agent routing patterns
• Testing skills

AGENTS.md Improvements

• Fix stale references (.opencode/commands/ → current reality)
• Add accurate directory map
• Add version number
• Add ecosystem overview (how agents, skills, commands, plugins, rules relate)

Acceptance Criteria

• docs/CONTRIBUTING.md created
• docs/authoring-agents.md created
• docs/authoring-skills.md created
• AGENTS.md updated with accurate references and ecosystem overview
• README.md updated with link to contribution guide