feat(todo): 子任务系统 — 复杂任务支持子任务拆解与依赖追踪

- 新增 `sub add <parent_id>` / `sub status <sid>` CLI 命令
- SID 格式 {parentId}{Letter}，支持依赖声明（deps）与校验
- HTML 新增子任务展开块、进度徽章、依赖色标（绿=完成/红=未完成）
- 父任务全部子任务完成时自动转为「待验收」；手动设 done 时检查子任务
- 更新 /todo 命令文档补充 sub 子命令说明
- #21 已录入 8 个实现子任务（21A–21H），含完整依赖链

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

todo/todo.json

@@ -1,9 +1,9 @@
 {
   "meta": {
     "title": "酒库管理系统 — 项目 TODO",
-    "updated_at": "2026-06-09T04:11:47.912Z"
+    "updated_at": "2026-06-09T16:15:09.789Z"
   },
-  "seq": 27,
+  "seq": 28,
   "items": [
     {
       "id": 1,
@@ -271,7 +271,7 @@
       "done": false,
       "completed_at": null,
       "version": null,
-      "status": "open"
+      "status": "done"
     },
     {
       "id": 21,
@@ -288,7 +288,92 @@
       "done": false,
       "completed_at": null,
       "version": null,
-      "status": "open"
+      "status": "doing",
+      "subtasks": [
+        {
+          "sid": "21A",
+          "title": "后端：Ed25519 签发验签工具 + GenerateKey 修复",
+          "tier": 2,
+          "deps": [],
+          "status": "open",
+          "created_at": "2026-06-09T16:14:58.628Z"
+        },
+        {
+          "sid": "21B",
+          "title": "数据库：license_devices 表 + licenses 表改造",
+          "tier": 2,
+          "deps": [
+            "21A"
+          ],
+          "status": "open",
+          "created_at": "2026-06-09T16:15:09.490Z"
+        },
+        {
+          "sid": "21C",
+          "title": "后端：注册自动签发 30 天 trial license",
+          "tier": 2,
+          "deps": [
+            "21A"
+          ],
+          "status": "open",
+          "created_at": "2026-06-09T16:15:09.541Z"
+        },
+        {
+          "sid": "21D",
+          "title": "后端：LicenseGuard 中间件 + JWT claim 扩展",
+          "tier": 2,
+          "deps": [
+            "21B",
+            "21C"
+          ],
+          "status": "open",
+          "created_at": "2026-06-09T16:15:09.590Z"
+        },
+        {
+          "sid": "21E",
+          "title": "前端：license model/repository/device_id 采集",
+          "tier": 2,
+          "deps": [
+            "21A"
+          ],
+          "status": "open",
+          "created_at": "2026-06-09T16:15:09.639Z"
+        },
+        {
+          "sid": "21F",
+          "title": "前端：激活与设备管理 UI（授权 Tab 重构）",
+          "tier": 2,
+          "deps": [
+            "21D",
+            "21E"
+          ],
+          "status": "open",
+          "created_at": "2026-06-09T16:15:09.689Z"
+        },
+        {
+          "sid": "21G",
+          "title": "前端：gating 横幅 + 到期弹窗（app_shell 注入）",
+          "tier": 2,
+          "deps": [
+            "21D",
+            "21E"
+          ],
+          "status": "open",
+          "created_at": "2026-06-09T16:15:09.739Z"
+        },
+        {
+          "sid": "21H",
+          "title": "端到端验证：phase 切换 + 签名拒绝 + 多设备上限",
+          "tier": 2,
+          "deps": [
+            "21D",
+            "21F",
+            "21G"
+          ],
+          "status": "open",
+          "created_at": "2026-06-09T16:15:09.789Z"
+        }
+      ]
     },
     {
       "id": 22,