feat(data): 废弃 usage 表 HTTP/结算列，迁移至 settlement_snapshots 与 http_audits

- 新增迁移 20260413030000：标记 billing_status、finalized_at、request_headers 等列为 DEPRECATED
- 更新 baseline_v2.sql 同步废弃注释，BASELINE_V2_CUTOFF_VERSION 升至 20260413030000
- usage/sql.rs：inline body 阈值归零，强制所有 body 走 blob 存储；upsert 时清空 legacy header/output_price 列
- 查询层优先读 usage_settlement_snapshots 的 billing_status、finalized_at、output_price_per_1m
- runtime.rs：stale usage 处理同步写入 usage_settlement_snapshots；SELECT FOR UPDATE 改为 FOR UPDATE OF usage
- 前端：PerformanceAnalysis 页面重构为实时面板，新增 prometheus 工具函数与 monitoring API

frontend/src/api/dashboard.ts

@@ -183,6 +183,18 @@ export interface RequestDetail {
   has_response_body?: boolean
   has_client_response_body?: boolean
   metadata?: Record<string, unknown>
+  settlement?: {
+    billing_snapshot?: Record<string, unknown>
+    billing_snapshot_schema_version?: string
+    billing_snapshot_status?: string
+    rate_multiplier?: number
+    is_free_tier?: boolean
+    input_price_per_1m?: number
+    output_price_per_1m?: number
+    cache_creation_price_per_1m?: number
+    cache_read_price_per_1m?: number
+    price_per_request?: number
+  } | null
   // 阶梯计费信息
   tiered_pricing?: {
     total_input_context: number  // 总输入上下文 (input + cache_read)