refactor: discriminated union frontmatter for solve-issue workflow
- planner: oneOf ready (plan, repoPath) | insufficient_info
- developer: single exit, plain object (branch, worktree), no $status
- reviewer: oneOf approved (branch, worktree) | rejected (comments)
- tester: oneOf passed (branch, worktree) | fix_code (report) | fix_spec (report)
- committer: oneOf committed (prUrl) | hook_failed (error)
- Edge prompts now use mustache templates with variant-specific fields
- Developer simplified from 2 exits to single exit (unit routing)
Phase 2 of #499 (closes #501)
xiaoju
827ff13c4a