refactor: migrate workflow system from 6-field nested to unified flat task schema

- Schema: add shared_context to plan-overview-base-schema, add pre_analysis/artifacts/inherited
  and polymorphic implementation (string|object with tdd_phase) to task-schema
- Producer: action-planning-agent outputs flat fields (description, depends_on, focus_paths,
  convergence.criteria, files, implementation, pre_analysis) + plan.json generation
- Orchestrator: plan.md/tdd-plan.md validate plan.json, task-generate-agent/tdd output dual-layer
- Consumer: code-developer/tdd-developer/test-fix-agent/universal-executor read flat fields
- Execute/review: read plan.json for execution strategy, use flat field paths
- Remove all migration notes referencing old field names

.claude/commands/workflow/review.md

@@ -186,8 +186,8 @@ After bash validation, the model takes control to:
      for task_file in ${sessionPath}/.task/*.json; do
        cat "$task_file" | jq -r '
          "Task: " + .id + "\n" +
-         "Requirements: " + (.context.requirements | join(", ")) + "\n" +
-         "Acceptance: " + (.context.acceptance | join(", "))
+         "Requirements: " + .description + "\n" +
+         "Acceptance: " + (.convergence.criteria | join(", "))
        '
      done