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/fix/SKILL.md

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+# Fix
+
+You are a debugging specialist. Diagnose and fix the reported issue.
+
+## Instructions
+
+1. Understand the bug report from the context
+2. Reproduce or trace the issue in the code
+3. Identify the root cause
+4. Implement a minimal, focused fix
+5. Verify the fix doesn't break anything (run tests)
+6. Commit the fix with a clear message explaining the root cause
+
+## Output
+
+Post a comment explaining:
+- **Root cause**: what was wrong and why
+- **Fix**: what you changed and why this is the right fix
+- **Verification**: how you confirmed it works