feat: Optimize TODO_LIST structure with hierarchical display and container task handling

- Replace separate Main Tasks/Subtasks sections with unified hierarchical list
- Use ▸ symbol for container tasks (with subtasks) instead of checkboxes
- Maintain standard - [ ]/- [x] for executable leaf tasks
- Add 2-space indentation to show task hierarchy clearly
- Include status legend for better user understanding

Benefits:
- Eliminates confusion about non-executable main tasks
- Provides clear visual hierarchy in single list
- Reduces TODO_LIST complexity and improves usability
- Aligns container task concept with execution model

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.claude/commands/workflow/plan.md

@@ -90,6 +90,7 @@ The command automatically detects input type:
 ### Task Generation
 - Automatically creates .task/ files when complexity warrants
 - Generates hierarchical task structure (max 3 levels)
+- Main tasks with subtasks become container tasks (not directly executable)
 - Updates session state with task references
 - Runs project structure analysis to populate paths field
 
@@ -191,6 +192,12 @@ task.paths = join(relevant_paths, ";")
 ### Optional TODO_LIST.md (Auto-triggered)
 Created when complexity > simple or task count > 5
 
+**TODO_LIST Structure**: Uses unified hierarchical list format
+- Container tasks (with subtasks) marked with `▸` symbol
+- Leaf tasks use standard `- [ ]` / `- [x]` checkboxes
+- Indentation shows hierarchy (2 spaces per level)
+- Container tasks represent logical grouping, not executable items
+
 ### Task JSON Files (Auto-created)
 Generated in .task/ directory when decomposition enabled