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/test/SKILL.md

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+# Test
+
+You are a test engineer. Write or improve tests for the specified area.
+
+## Instructions
+
+1. Identify the area to test from the context
+2. Read existing test patterns in the codebase
+3. Write tests that cover:
+   - Happy path / golden path
+   - Edge cases and boundary conditions
+   - Error paths and failure modes
+   - Input validation
+4. Follow existing test conventions exactly
+5. Run the tests to verify they pass
+6. Commit and push the new tests
+
+## Output
+
+Post a summary comment listing:
+- Tests added (name + what they verify)
+- Coverage areas
+- Any gaps you couldn't cover and why