feat(proxy): T-P7 管理面前端（ProxyView 三卡片 + 路由/NAV 注册）

- webapp/api：getProxyStats/getProxyLedger/listProxyStudents/createStudent/
  topup/issueKey/revokeKey 封装
- ProxyView.vue 三卡片：① 命中率-毛利看板（h_g/h_p/综合/收入/成本/毛利/分桶）
  ② 学生与 key 管理（建学生/签发（明文仅显一次警示）/充值/选中签发）
  ③ 用量流水表（时间/模型/状态徽标/收入/成本/毛利）
- App.vue NAV + router 注册 /proxy；npm run build 产物更新
- 全量 423 passed

webapp/.mimosa/hook-status/sess_e50d4f25-3ac6-43f2-b2f3-8833b3150465-4843032ba9.json

@@ -1,14 +1,14 @@
 {
   "schemaVersion": "mimosa-hook-status/v1",
-  "recordedAt": "2026-09-05T07:03:44.339Z",
+  "recordedAt": "2026-09-05T08:17:05.111Z",
   "sessionId": "sess_e50d4f25-3ac6-43f2-b2f3-8833b3150465",
   "event": "PostToolUse",
   "toolName": "Edit",
-  "file": "src/views/MetricsView.vue",
+  "file": "src/App.vue",
   "outcome": "clear",
   "coverage": "complete",
   "findingCount": 0,
-  "durationMs": 2,
+  "durationMs": 3,
   "hostState": "hook_complete",
   "reportHint": ".mimosa/reports/"
 }