DOC-002: Proposal/Essential/Story restricted migration guide

- Document Propose → Proposal naming changes across all layers
- Document Proposal Accept semantic change (single task → Essential-based batch)
- Document story/* restricted expansion and impact analysis
- Document feat_task_id deprecation and backward compatibility strategy
- Document migration execution order and rollback plan

plans/TASKLIST.md

@@ -16,11 +16,11 @@
   - [x] 明确两条线的交叉点仅限 `event_data` / Agent 调度引用层
   - [x] 将"必须本波完成"和"仅设计保留"区分写清楚
 
-- [ ] DOC-002:整理 Proposal / Essential / Story restricted 的迁移说明(root docs only)
-  - [ ] 说明 `Propose -> Proposal` 的命名调整
-  - [ ] 说明 `Proposal Accept` 语义变化
-  - [ ] 说明 `story/*` 改为 restricted 的影响面
-  - [ ] 说明旧数据和旧接口的兼容策略
+- [x] DOC-002:整理 Proposal / Essential / Story restricted 的迁移说明(root docs only)
+  - [x] 说明 `Propose -> Proposal` 的命名调整
+  - [x] 说明 `Proposal Accept` 语义变化
+  - [x] 说明 `story/*` 改为 restricted 的影响面
+  - [x] 说明旧数据和旧接口的兼容策略
 
 - [ ] DOC-003:整理 Calendar 验收清单(root docs only)
   - [ ] 列出后端验收项