feat: add gitagent format for cross-harness portability

RULES.md

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+# Rules
+
+## Must Always
+- Delegate to specialized agents for domain tasks.
+- Write tests before implementation and verify critical paths.
+- Validate inputs and keep security checks intact.
+- Prefer immutable updates over mutating shared state.
+- Follow established repository patterns before inventing new ones.
+- Keep contributions focused, reviewable, and well-described.
+
+## Must Never
+- Include sensitive data such as API keys, tokens, secrets, or absolute/system file paths in output.
+- Submit untested changes.
+- Bypass security checks or validation hooks.
+- Duplicate existing functionality without a clear reason.
+- Ship code without checking the relevant test suite.
+
+## Agent Format
+- Agents live in `agents/*.md`.
+- Each file includes YAML frontmatter with `name`, `description`, `tools`, and `model`.
+- File names are lowercase with hyphens and must match the agent name.
+- Descriptions must clearly communicate when the agent should be invoked.
+
+## Skill Format
+- Skills live in `skills/<name>/SKILL.md`.
+- Each skill includes YAML frontmatter with `name`, `description`, and `origin`.
+- Use `origin: ECC` for first-party skills and `origin: community` for imported/community skills.
+- Skill bodies should include practical guidance, tested examples, and clear "When to Use" sections.
+
+## Hook Format
+- Hooks use matcher-driven JSON registration and shell or Node entrypoints.
+- Matchers should be specific instead of broad catch-alls.
+- Exit `1` only when blocking behavior is intentional; otherwise exit `0`.
+- Error and info messages should be actionable.
+
+## Commit Style
+- Use conventional commits such as `feat(skills):`, `fix(hooks):`, or `docs:`.
+- Keep changes modular and explain user-facing impact in the PR summary.