docs(admin): 补充管理后台 API 与数据库文档 (#12)

新增 admin 模块接口文档(auth login/me、admins CRUD、audit-logs、feedback 处理、stats 概览、user coins/detail/status、wallet 流水、withdraw 对账/刷新/列表) + admin_user/admin_audit_log 两张表文档，更新 api/database README 索引。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: OuYingJun1024 <1034284404@qq.com>
Reviewed-on: #12
Co-authored-by: ouzhou <ouzhou@wonderable.ai>
Co-committed-by: ouzhou <ouzhou@wonderable.ai>

tests/test_welfare.py

@@ -133,10 +133,10 @@ def test_exchange_info(client) -> None:
 
 
 def test_exchange_flow(client) -> None:
-    """先供款够兑换下限的金币 → 兑换 1 元 → 金币扣、现金加 → 现金流水有记录。
+    """先供款够兑 1 元的金币 → 兑换 1 元 → 金币扣、现金加 → 现金流水有记录。
 
-    打开消息提醒任务已降到 1000 金币(不再 = 兑换下限), 不能再靠领任务供款;
-    直接 grant_coins 注入 MIN_EXCHANGE_COIN(= COIN_PER_YUAN = 10000)当种子。
+    兑换下限已降到 1 分(MIN_EXCHANGE_COIN = COIN_PER_CENT = 100), 但本用例验证兑换 1 元,
+    直接 grant_coins 注入 COIN_PER_YUAN(= 10000)当种子(够兑 1 元)。
     """
     phone = "13800001005"
     token = _login(client, phone)
@@ -144,7 +144,7 @@ def test_exchange_flow(client) -> None:
     with SessionLocal() as db:
         user = get_user_by_phone(db, phone)
         assert user is not None
-        crud_wallet.grant_coins(db, user.id, MIN_EXCHANGE_COIN, biz_type="test_seed", remark="测试供款")
+        crud_wallet.grant_coins(db, user.id, COIN_PER_YUAN, biz_type="test_seed", remark="测试供款")
         db.commit()
 
     # 兑换 10000 金币 → 100 分
@@ -180,6 +180,51 @@ def test_exchange_flow(client) -> None:
     assert page["items"][0]["biz_type"] == "exchange_in"
 
 
+def test_exchange_min_floor_one_cent(client) -> None:
+    """锁定本次下调的兑换下限:正好兑下限额(MIN_EXCHANGE_COIN=100 金币=1 分)应成功。
+
+    这是本 PR 的核心新能力(下限 10000→100,可兑 1 分起)。test_exchange_flow 兑的是
+    1 元(10000),在旧下限下也通过,证明不了新下限;本用例供款并兑换正好等于下限的
+    100 金币,断言到账 1 分。若有人把 MIN_EXCHANGE_COIN 改回 10000,100 会因低于下限被
+    判 400,本用例随之失败,从而把新下限值钉死。
+    """
+    phone = "13800001010"
+    token = _login(client, phone)
+    # 供款: 正好注入一个下限额度的金币(=COIN_PER_CENT=100)
+    with SessionLocal() as db:
+        user = get_user_by_phone(db, phone)
+        assert user is not None
+        crud_wallet.grant_coins(
+            db, user.id, MIN_EXCHANGE_COIN, biz_type="test_seed", remark="测试供款"
+        )
+        db.commit()
+
+    # 兑换下限额 100 金币 → 1 分
+    r = client.post(
+        "/api/v1/wallet/exchange",
+        json={"coin_amount": MIN_EXCHANGE_COIN},
+        headers=_auth(token),
+    )
+    assert r.status_code == 200, r.text
+    res = r.json()
+    assert res["coin_amount"] == MIN_EXCHANGE_COIN
+    assert res["cash_added_cents"] == 1  # coins_to_cents(100) == 1
+    assert res["coin_balance"] == 0
+    assert res["cash_balance_cents"] == 1
+
+    # 金币流水有一笔 exchange_out(=-100)
+    r = client.get("/api/v1/wallet/coin-transactions", headers=_auth(token))
+    out_txn = next(t for t in r.json()["items"] if t["biz_type"] == "exchange_out")
+    assert out_txn["amount"] == -MIN_EXCHANGE_COIN
+
+    # 现金流水有且仅有一笔 exchange_in(=+1 分)
+    r = client.get("/api/v1/wallet/cash-transactions", headers=_auth(token))
+    cash = r.json()["items"]
+    assert len(cash) == 1
+    assert cash[0]["amount_cents"] == 1
+    assert cash[0]["biz_type"] == "exchange_in"
+
+
 def test_exchange_insufficient_and_invalid(client) -> None:
     token = _login(client, "13800001006")
 
@@ -191,10 +236,10 @@ def test_exchange_insufficient_and_invalid(client) -> None:
     )
     assert r.status_code == 409
 
-    # 低于最小额 → 400
+    # 低于最小额(下限现为 1 分=100;取 MIN_EXCHANGE_COIN-1=99,既低于下限又非整分)→ 400
     r = client.post(
         "/api/v1/wallet/exchange",
-        json={"coin_amount": MIN_EXCHANGE_COIN - COIN_PER_CENT},
+        json={"coin_amount": MIN_EXCHANGE_COIN - 1},
         headers=_auth(token),
     )
     assert r.status_code == 400
@@ -226,6 +271,8 @@ def test_savings_summary_and_battle(client) -> None:
     assert b["streak_days"] >= 1
     assert b["week_saved_cents"] >= 0
     assert 0 <= b["beat_percent"] <= 100
+    # 完成比价次数与 summary 的 order_count 同源(均 = 有效记录数)
+    assert b["compare_count"] == s["order_count"]
 
 
 def test_savings_seeder_idempotent(client) -> None: