BE-PR-001: Rename Propose -> Proposal across backend

- Backend: new canonical Proposal model + /proposals router
- Backward-compat shims for old Propose imports and /proposes API
- Tests updated to use /proposals, legacy compat tests added
- Impact checklist: docs/BE-PR-001-rename-impact.md
- TASKLIST.md: BE-PR-001 marked complete

All 21 proposal tests pass.

plans/TASKLIST.md

@@ -30,10 +30,10 @@
 
 ## B. HarborForge.Backend - Proposal / Essential / Story restricted
 
-- [ ] BE-PR-001:后端统一重命名 `Propose` 概念为 `Proposal`(backend only)
-  - [ ] 盘点 `models / schemas / routers / services / tests` 中 `propose` 命名
-  - [ ] 明确保留兼容别名还是直接切换
-  - [ ] 输出重命名影响清单
+- [x] BE-PR-001:后端统一重命名 `Propose` 概念为 `Proposal`(backend only)
+  - [x] 盘点 `models / schemas / routers / services / tests` 中 `propose` 命名
+  - [x] 明确保留兼容别名还是直接切换 → 保留别名 + legacy API 路由
+  - [x] 输出重命名影响清单 → `docs/BE-PR-001-rename-impact.md`
 
 - [ ] BE-PR-002:新增 Proposal 数据模型调整(backend only)
   - [ ] 调整 Proposal 模型命名与字段注释