fix: throttle Anthropic usage queries and pass through upstream HTTP errors

- Frontend: queue Anthropic OAuth/setup-token usage requests by proxy
  with random 1-1.5s interval to prevent upstream 429
- Backend: return ApplicationError with actual upstream status code
  instead of wrapping all errors as 500
- Handle component unmount to skip stale updates on page navigation

frontend/src/utils/__tests__/usageLoadQueue.spec.ts

@@ -0,0 +1,87 @@
+import { describe, expect, it, vi } from 'vitest'
+import { enqueueUsageRequest } from '../usageLoadQueue'
+
+function delay(ms: number) {
+  return new Promise((r) => setTimeout(r, ms))
+}
+
+describe('usageLoadQueue', () => {
+  it('同组请求串行执行，间隔 >= 1s', async () => {
+    const timestamps: number[] = []
+    const makeFn = () => async () => {
+      timestamps.push(Date.now())
+      return 'ok'
+    }
+
+    const p1 = enqueueUsageRequest('anthropic', 'oauth', 1, makeFn())
+    const p2 = enqueueUsageRequest('anthropic', 'oauth', 1, makeFn())
+    const p3 = enqueueUsageRequest('anthropic', 'oauth', 1, makeFn())
+
+    await Promise.all([p1, p2, p3])
+
+    expect(timestamps).toHaveLength(3)
+    // 随机 1-1.5s 间隔，至少 950ms（留一点误差）
+    expect(timestamps[1] - timestamps[0]).toBeGreaterThanOrEqual(950)
+    expect(timestamps[1] - timestamps[0]).toBeLessThan(1600)
+    expect(timestamps[2] - timestamps[1]).toBeGreaterThanOrEqual(950)
+    expect(timestamps[2] - timestamps[1]).toBeLessThan(1600)
+  })
+
+  it('不同组请求并行执行', async () => {
+    const timestamps: Record<string, number> = {}
+    const makeTracked = (key: string) => async () => {
+      timestamps[key] = Date.now()
+      return key
+    }
+
+    const p1 = enqueueUsageRequest('anthropic', 'oauth', 1, makeTracked('group1'))
+    const p2 = enqueueUsageRequest('anthropic', 'oauth', 2, makeTracked('group2'))
+    const p3 = enqueueUsageRequest('gemini', 'oauth', 1, makeTracked('group3'))
+
+    await Promise.all([p1, p2, p3])
+
+    // 不同组应几乎同时启动（差距 < 50ms）
+    const values = Object.values(timestamps)
+    const spread = Math.max(...values) - Math.min(...values)
+    expect(spread).toBeLessThan(50)
+  })
+
+  it('请求失败时 reject，后续任务继续执行', async () => {
+    const results: string[] = []
+
+    const p1 = enqueueUsageRequest('anthropic', 'oauth', 99, async () => {
+      throw new Error('fail')
+    })
+    const p2 = enqueueUsageRequest('anthropic', 'oauth', 99, async () => {
+      results.push('second')
+      return 'ok'
+    })
+
+    await expect(p1).rejects.toThrow('fail')
+    await p2
+    expect(results).toEqual(['second'])
+  })
+
+  it('返回值正确透传', async () => {
+    const result = await enqueueUsageRequest('test', 'oauth', null, async () => {
+      return { usage: 42 }
+    })
+    expect(result).toEqual({ usage: 42 })
+  })
+
+  it('proxy_id 为 null 的账号归为同一组', async () => {
+    const order: number[] = []
+    const makeFn = (n: number) => async () => {
+      order.push(n)
+      return n
+    }
+
+    const p1 = enqueueUsageRequest('anthropic', 'oauth', null, makeFn(1))
+    const p2 = enqueueUsageRequest('anthropic', 'oauth', null, makeFn(2))
+
+    await Promise.all([p1, p2])
+
+    // 同组串行，按入队顺序执行
+    expect(order).toEqual([1, 2])
+  })
+})