fix(test): 修复测试和添加数据库迁移

测试修复：
- 修复集成测试中的重复键冲突问题
- 移除 JSON 中多余的尾随逗号
- 新增 inprocess_transport_test.go
- 更新 haiku 模型映射测试用例

数据库迁移：
- 026: 运营指标聚合表
- 027: 使用量与计费一致性约束

backend/migrations/027_usage_billing_consistency.sql

@@ -0,0 +1,58 @@
+-- 027_usage_billing_consistency.sql
+-- Ensure usage_logs idempotency (request_id, api_key_id) and add reconciliation infrastructure.
+
+-- -----------------------------------------------------------------------------
+-- 1) Normalize legacy request_id values
+-- -----------------------------------------------------------------------------
+-- Historically request_id may be inserted as empty string. Convert it to NULL so
+-- the upcoming unique index does not break on repeated "" values.
+UPDATE usage_logs
+SET request_id = NULL
+WHERE request_id = '';
+
+-- If duplicates already exist for the same (request_id, api_key_id), keep the
+-- first row and NULL-out request_id for the rest so the unique index can be
+-- created without deleting historical logs.
+WITH ranked AS (
+    SELECT
+        id,
+        ROW_NUMBER() OVER (PARTITION BY api_key_id, request_id ORDER BY id) AS rn
+    FROM usage_logs
+    WHERE request_id IS NOT NULL
+)
+UPDATE usage_logs ul
+SET request_id = NULL
+FROM ranked r
+WHERE ul.id = r.id
+  AND r.rn > 1;
+
+-- -----------------------------------------------------------------------------
+-- 2) Idempotency constraint for usage_logs
+-- -----------------------------------------------------------------------------
+CREATE UNIQUE INDEX IF NOT EXISTS idx_usage_logs_request_id_api_key_unique
+    ON usage_logs (request_id, api_key_id);
+
+-- -----------------------------------------------------------------------------
+-- 3) Reconciliation infrastructure: billing ledger for usage charges
+-- -----------------------------------------------------------------------------
+CREATE TABLE IF NOT EXISTS billing_usage_entries (
+    id BIGSERIAL PRIMARY KEY,
+    usage_log_id BIGINT NOT NULL REFERENCES usage_logs(id) ON DELETE CASCADE,
+    user_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    api_key_id BIGINT NOT NULL REFERENCES api_keys(id) ON DELETE CASCADE,
+    subscription_id BIGINT REFERENCES user_subscriptions(id) ON DELETE SET NULL,
+    billing_type SMALLINT NOT NULL,
+    applied BOOLEAN NOT NULL DEFAULT TRUE,
+    delta_usd DECIMAL(20, 10) NOT NULL DEFAULT 0,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS billing_usage_entries_usage_log_id_unique
+    ON billing_usage_entries (usage_log_id);
+
+CREATE INDEX IF NOT EXISTS idx_billing_usage_entries_user_time
+    ON billing_usage_entries (user_id, created_at);
+
+CREATE INDEX IF NOT EXISTS idx_billing_usage_entries_created_at
+    ON billing_usage_entries (created_at);
+