收紧后端 TypeScript：统一 Json 类型与 TaskContext 契约

关闭 allowJs；集中 JsonObject 定义并替换分散 any 别名；parseTaskContext 返回 TaskContext；任务详情 API 标注 AdminTaskDetailView；测试减少 as any。

apps/backend/tsconfig.json

@@ -3,8 +3,8 @@
     "target": "ES2022",
     "module": "NodeNext",
     "moduleResolution": "NodeNext",
-    "allowJs": true,
-    "checkJs": true,
+    "allowJs": false,
+    "checkJs": false,
     "noEmit": true,
     "strict": true,
     "noUncheckedIndexedAccess": true,
@@ -14,13 +14,11 @@
     "lib": ["ES2022"]
   },
   "include": [
-    "src/**/*.js",
     "src/**/*.ts"
   ],
   "exclude": [
     "node_modules",
     "data",
-    "src/**/*.test.js",
     "src/**/*.test.ts"
   ]
 }