feat(workflow): add workflow:replan command with session-level replanning support

## Changes

### New Command: workflow:replan
- Created `.claude/commands/workflow/replan.md` with comprehensive session-level replanning
- Supports dual modes: session-wide and task-specific replanning
- Interactive boundary clarification using guided questioning
- Updates multiple artifacts: IMPL_PLAN.md, TODO_LIST.md, task JSONs, session metadata
- Comprehensive backup management with restore capability

### Key Features
1. **Interactive Clarification**: Guided questions to define modification scope
   - Modification scope (tasks only, plan update, task restructure, comprehensive)
   - Affected modules detection
   - Task change types (add, remove, merge, split, update)
   - Dependency relationship updates

2. **Session-Aware Operations**:
   - Auto-detects active sessions from `.workflow/active/`
   - Updates all session artifacts consistently
   - Maintains backup history in `.process/backup/replan-{timestamp}/`

3. **Comprehensive Artifact Updates**:
   - IMPL_PLAN.md section modifications
   - TODO_LIST.md task list updates
   - Task JSON files (requirements, implementation, dependencies)
   - Session metadata tracking

4. **Impact Analysis**: Automatically determines affected files and operations

### Deprecation
- Added deprecation notice to `/task:replan` in both command and reference files
- Updated `COMMAND_REFERENCE.md` to:
  - Add workflow:replan to Core Workflow section
  - Mark task:replan as deprecated with migration guidance

### Migration Path
- Old: `/task:replan IMPL-1 "changes"`
- New: `/workflow:replan IMPL-1 "changes"`

### Files Modified
- `.claude/commands/task/replan.md`: Added deprecation notice
- `.claude/commands/workflow/replan.md`: New command implementation
- `.claude/skills/command-guide/reference/commands/task/replan.md`: Deprecation notice
- `.claude/skills/command-guide/reference/commands/workflow/replan.md`: Reference documentation
- `COMMAND_REFERENCE.md`: Updated command listings

This change enhances workflow replanning capabilities by providing interactive,
session-aware modifications that maintain consistency across all workflow artifacts.

.claude/commands/task/replan.md

@@ -7,6 +7,14 @@ allowed-tools: Read(*), Write(*), Edit(*), TodoWrite(*), Glob(*), Bash(*)
 
 # Task Replan Command (/task:replan)
 
+> **⚠️ DEPRECATION NOTICE**: This command is maintained for backward compatibility. For new workflows, use `/workflow:replan` which provides:
+> - Session-level replanning with comprehensive artifact updates
+> - Interactive boundary clarification
+> - Updates to IMPL_PLAN.md, TODO_LIST.md, and session metadata
+> - Better integration with workflow sessions
+>
+> **Migration**: Replace `/task:replan IMPL-1 "changes"` with `/workflow:replan IMPL-1 "changes"`
+
 ## Overview
 Replans individual tasks or batch processes multiple tasks with change tracking and backup management.