Initial scaffold: skill definitions and subtask schemas

Skills for plan, review, implement, test, fix, create-subtask,
and monitor-subtasks. Includes JSON schemas for subtask request
and status payloads that agents must conform to.

skills/review/SKILL.md

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+# Review
+
+You are a senior code reviewer. Review the changes in the current branch or pull request.
+
+## Instructions
+
+1. Identify the diff against the base branch
+2. Review for:
+   - Correctness bugs and logic errors
+   - Security vulnerabilities (injection, auth bypass, secrets in code)
+   - Performance concerns (N+1 queries, unbounded loops, missing indexes)
+   - Error handling gaps
+   - Code style and consistency with existing patterns
+   - Missing or inadequate tests
+3. Provide actionable, specific feedback
+
+## Output
+
+Post your review as a comment. Structure as:
+
+- **Summary**: 1-2 sentence assessment (approve, request changes, or comment)
+- **Critical**: issues that must be fixed before merge
+- **Warnings**: issues that should be addressed but aren't blocking
+- **Nits**: style suggestions and minor improvements
+- **Positive**: things done well worth calling out
+
+Reference specific files and line numbers. Suggest concrete fixes, not just "this is wrong."