feat: 添加 provider usage 统计与余额查询

- 新增 providerUsage 服务（anthropic/bedrock/openai 适配器）
- 新增余额查询（deepseek/generic poller）
- StatusLine 保留原有 rateLimits 接口不变

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/services/providerUsage/balance/poller.ts

@@ -0,0 +1,78 @@
+import { setProviderBalance } from '../store.js'
+import { deepseekBalanceProvider } from './deepseek.js'
+import { genericBalanceProvider } from './generic.js'
+import type { BalanceProvider } from './types.js'
+
+const DEFAULT_INTERVAL_MIN = 10
+
+// Registration order = priority. First enabled wins. Generic (user-supplied
+// URL) comes first so operators can override the built-in DeepSeek detection.
+const PROVIDERS: BalanceProvider[] = [
+  genericBalanceProvider,
+  deepseekBalanceProvider,
+]
+
+function selectProvider(): BalanceProvider | null {
+  if (process.env.CLAUDE_CODE_BALANCE_PROVIDER === 'none') return null
+  return PROVIDERS.find(p => p.isEnabled()) ?? null
+}
+
+function intervalMs(): number {
+  const raw = process.env.CLAUDE_CODE_BALANCE_POLL_INTERVAL_MINUTES
+  const n = raw ? Number(raw) : DEFAULT_INTERVAL_MIN
+  if (!Number.isFinite(n) || n <= 0) return DEFAULT_INTERVAL_MIN * 60_000
+  return Math.floor(n * 60_000)
+}
+
+let timer: ReturnType<typeof setInterval> | null = null
+let inflight: AbortController | null = null
+let active: BalanceProvider | null = null
+
+const FETCH_TIMEOUT_MS = 10_000
+
+async function tick(): Promise<void> {
+  if (!active) return
+  inflight?.abort()
+  inflight = new AbortController()
+  const timeout = setTimeout(() => inflight?.abort(), FETCH_TIMEOUT_MS)
+  try {
+    const balance = await active.fetchBalance(inflight.signal)
+    setProviderBalance(active.providerId, balance)
+  } catch {
+    // Never bubble into the host process.
+  } finally {
+    clearTimeout(timeout)
+  }
+}
+
+/** Start polling if a provider is configured. Idempotent. */
+export function startBalancePolling(): void {
+  if (timer !== null) return
+  active = selectProvider()
+  if (!active) return
+  // Kick off immediately, then on interval.
+  void tick()
+  timer = setInterval(() => {
+    void tick()
+  }, intervalMs())
+  // Don't keep the event loop alive just for the poller.
+  if (
+    typeof (timer as unknown as { unref?: () => void }).unref === 'function'
+  ) {
+    ;(timer as unknown as { unref: () => void }).unref()
+  }
+}
+
+export function stopBalancePolling(): void {
+  if (timer !== null) {
+    clearInterval(timer)
+    timer = null
+  }
+  inflight?.abort()
+  inflight = null
+  active = null
+}
+
+export function getActiveBalanceProviderId(): string | null {
+  return active?.providerId ?? null
+}