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/utils/__tests__/prometheus.spec.ts

@@ -0,0 +1,37 @@
+import { describe, expect, it } from 'vitest'
+import {
+  findMetricValueNumber,
+  parsePrometheusSamples,
+  sumMetricValues,
+} from '../prometheus'
+
+describe('parsePrometheusSamples', () => {
+  it('parses labeled samples and finds gate metrics by suffix name', () => {
+    const samples = parsePrometheusSamples(`
+# HELP aether_gateway_concurrency_in_flight Current number of in-flight operations.
+# TYPE aether_gateway_concurrency_in_flight gauge
+aether_gateway_concurrency_in_flight{gate="gateway_requests"} 7
+aether_gateway_concurrency_rejected_total{gate="gateway_requests"} 12
+`)
+
+    expect(
+      findMetricValueNumber(samples, 'concurrency_in_flight', {
+        gate: 'gateway_requests',
+      })
+    ).toBe(7)
+    expect(
+      findMetricValueNumber(samples, 'concurrency_rejected_total', {
+        gate: 'gateway_requests',
+      })
+    ).toBe(12)
+  })
+
+  it('sums fallback counters across labeled samples', () => {
+    const samples = parsePrometheusSamples(`
+decision_remote_total{route_kind="chat",reason="local_decision_miss"} 2
+decision_remote_total{route_kind="responses",reason="remote_decision_miss"} 3
+`)
+
+    expect(sumMetricValues(samples, 'decision_remote_total')).toBe(5)
+  })
+})

frontend/src/utils/prometheus.ts

@@ -0,0 +1,106 @@
+export interface PrometheusSample {
+  name: string
+  labels: Record<string, string>
+  value: string
+}
+
+export function parsePrometheusSamples(text: string): PrometheusSample[] {
+  return text
+    .split(/\r?\n/)
+    .map(line => line.trim())
+    .filter(line => line.length > 0 && !line.startsWith('#'))
+    .map(parsePrometheusLine)
+    .filter((sample): sample is PrometheusSample => sample !== null)
+}
+
+export function findMetricValueNumber(
+  samples: PrometheusSample[],
+  metricName: string,
+  labels: Record<string, string> = {}
+): number | null {
+  const sample = samples.find(item =>
+    metricNameMatches(item.name, metricName) && labelsMatch(item.labels, labels)
+  )
+
+  if (!sample) {
+    return null
+  }
+
+  const value = Number(sample.value)
+  return Number.isFinite(value) ? value : null
+}
+
+export function sumMetricValues(
+  samples: PrometheusSample[],
+  metricName: string
+): number {
+  return samples.reduce((total, sample) => {
+    if (!metricNameMatches(sample.name, metricName)) {
+      return total
+    }
+
+    const value = Number(sample.value)
+    return Number.isFinite(value) ? total + value : total
+  }, 0)
+}
+
+function metricNameMatches(actual: string, expected: string): boolean {
+  return actual === expected || actual.split('_').pop() === expected || actual.endsWith(`_${expected}`)
+}
+
+function labelsMatch(
+  actual: Record<string, string>,
+  expected: Record<string, string>
+): boolean {
+  return Object.entries(expected).every(([key, value]) => actual[key] === value)
+}
+
+function parsePrometheusLine(line: string): PrometheusSample | null {
+  const separatorIndex = line.lastIndexOf(' ')
+  if (separatorIndex === -1) {
+    return null
+  }
+
+  const metric = line.slice(0, separatorIndex).trim()
+  const value = line.slice(separatorIndex + 1).trim()
+  if (!metric || !value) {
+    return null
+  }
+
+  const labelStart = metric.indexOf('{')
+  if (labelStart === -1 || !metric.endsWith('}')) {
+    return {
+      name: metric,
+      labels: {},
+      value,
+    }
+  }
+
+  return {
+    name: metric.slice(0, labelStart),
+    labels: parseLabels(metric.slice(labelStart + 1, -1)),
+    value,
+  }
+}
+
+function parseLabels(raw: string): Record<string, string> {
+  const labels: Record<string, string> = {}
+  const pattern = /([^=,\s]+)="((?:\\.|[^"])*)"/g
+
+  for (const match of raw.matchAll(pattern)) {
+    const [, key, value] = match
+    if (!key) {
+      continue
+    }
+    labels[key] = unescapePrometheusLabel(value ?? '')
+  }
+
+  return labels
+}
+
+function unescapePrometheusLabel(value: string): string {
+  return value
+    .replace(/\\"/g, '"')
+    .replace(/\\n/g, '\n')
+    .replace(/\\\\/g, '\\')
+}