@

docs: reorganize api docs into categorized subdirectories and fill missing docs

- Categorize 77 existing api docs into 16 business-domain subdirectories
  (auth/ad/wallet/coupon/compare/savings/signin/tasks/invite/user/
   device/platform/intent/meituan/other) plus admin/ and internal/
- Split admin/ into 7 sub-resource subdirectories (auth/users/wallet/
  withdraws/feedbacks/admins/ad) with 4 single-file docs at root
- Create 21 new docs covering 28 previously undocumented endpoints:
  ad/watch-report, wallet/transfer-auth (3 endpoints), coupon/session+
  stats+completed-today+prompt (7), invite/me+invitees+bind+landing-track,
  user/onboarding (2), platform/flags+ad-config+app-version,
  intent/step+precoupon/step, analytics/events, order/report,
  report/submit+records, feedback/config+records, trace/finalize
- Add mock request/response JSON examples to all new docs
- Create docs/README.md with full category index for LLM navigation
- Update docs/api/README.md: fix all links, add new endpoint rows,
  replace "no doc" markers with actual links
- Fix back-navigation links (./README.md -> ../README.md or
  ../../README.md) in all moved files
@

docs/api/wallet/wallet-exchange.md

@@ -0,0 +1,26 @@
+# POST /api/v1/wallet/exchange — 金币兑现金
+
+> 所属:Wallet 组（前缀 `/api/v1/wallet`） | 鉴权:Bearer | [← 返回 API 索引](../README.md)
+
+## 入参
+
+| 字段 | 类型 | 必填 | 说明 |
+|---|---|---|---|
+| `coin_amount` | int | ✅（>0） | 要兑换的金币数,须 ≥ `min_coin` 且为 `step_coin` 整数倍 |
+
+## 出参
+响应 `200`:`ExchangeResultOut`
+
+| 字段 | 类型 | 说明 |
+|---|---|---|
+| `coin_amount` | int | 本次扣除的金币 |
+| `cash_added_cents` | int | 本次兑入的现金（分） |
+| `coin_balance` | int | 兑换后金币余额 |
+| `cash_balance_cents` | int | 兑换后现金余额（分） |
+
+## 错误码
+- `400` `coin_amount` 不满足 ≥ `min_coin` 且为 `step_coin` 整数倍
+- `409` 金币余额不足
+
+## 说明
+兑换规则见 [wallet-exchange-info](./wallet-exchange-info.md)。金币与现金的扣加在同一事务内完成。