feat(backend): refactor OCR client to support HTTP + subprocess dual mode

- runtime-config.js: add baseUrl field to ocr type definition
- default.cjs: add ocr.baseUrl default (empty string = subprocess mode)
- runtime.js: add OCR_BASE_URL env var parsing
- ocr.js: add HTTP mode (when OCR_BASE_URL set) alongside existing subprocess mode
  - resolveOcrMode() detects mode from runtimeConfig.ocr.baseUrl
  - callOcrViaHttp() calls FastAPI endpoints directly with payload
  - warmupOcrViaHttp() calls /health endpoint for HTTP mode warmup
  - callOcrRequest() routes between HTTP and subprocess based on mode
  - All 5 original exports preserved (recognizeTencentCaptcha, etc.)
  - Subprocess mode remains backward compatible (default when no OCR_BASE_URL)

apps/backend/src/services/session/ocr.js

@@ -22,14 +22,89 @@ export async function batchRecognizeTencentCaptcha(payload) {
 }
 
 export async function warmupLocalOcrWorker() {
+  const mode = resolveOcrMode()
+  if (mode === 'http') {
+    await warmupOcrViaHttp()
+    return
+  }
   await runOcrCommand('healthcheck', { timeoutMs: 30_000 })
 }
 
 export async function closeLocalOcrWorker() {
-  // OCR 改为按次调用 Python 子进程，这里不再维护常驻 worker。
+  // OCR 改为按次调用 Python 子进程或 HTTP 服务，这里不再维护常驻 worker。
 }
 
+// ── Mode Resolution ──────────────────────────────────────────────────────────
+
+function resolveOcrMode() {
+  if (String(runtimeConfig.ocr.baseUrl || '').trim()) {
+    return 'http'
+  }
+  return 'subprocess'
+}
+
+// ── HTTP Mode ─────────────────────────────────────────────────────────────────
+
+async function callOcrViaHttp(action, payload, { timeoutMs }) {
+  const baseUrl = String(runtimeConfig.ocr.baseUrl).trim().replace(/\/+$/, '')
+  const url = `${baseUrl}/ocr/${action}`
+
+  let response
+  try {
+    response = await fetch(url, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(payload),
+      signal: AbortSignal.timeout(timeoutMs),
+    })
+  } catch (err) {
+    if (err instanceof Error && err.name === 'TimeoutError') {
+      throw new Error(`OCR 请求超时（${timeoutMs}ms），请检查 OCR 服务状态`)
+    }
+    throw new Error(`OCR 服务不可用（${baseUrl}），请检查 ocr-worker 容器是否正常运行`)
+  }
+
+  if (!response.ok) {
+    throw new Error(`OCR 服务返回错误：HTTP ${response.status}`)
+  }
+
+  const result = await response.json()
+  if (!result || typeof result !== 'object' || Array.isArray(result)) {
+    throw new Error('OCR 服务返回了无效响应')
+  }
+  if (result.code !== 0) {
+    throw new Error(`OCR 服务返回错误：${result.msg || '未知错误'}`)
+  }
+
+  return result
+}
+
+async function warmupOcrViaHttp() {
+  const baseUrl = String(runtimeConfig.ocr.baseUrl).trim().replace(/\/+$/, '')
+  let response
+  try {
+    response = await fetch(`${baseUrl}/health`, {
+      signal: AbortSignal.timeout(30_000),
+    })
+  } catch (err) {
+    if (err instanceof Error && err.name === 'TimeoutError') {
+      throw new Error(`OCR 服务健康检查超时，请检查 ${baseUrl} 是否可访问`)
+    }
+    throw new Error(`OCR 服务不可用（${baseUrl}），请检查 ocr-worker 容器是否正常运行`)
+  }
+  if (!response.ok) {
+    throw new Error(`OCR 服务健康检查失败：HTTP ${response.status}`)
+  }
+}
+
+// ── Request Router ────────────────────────────────────────────────────────────
+
 async function callOcrRequest(action, payload, { timeoutMs = DEFAULT_TIMEOUT_MS } = {}) {
+  const mode = resolveOcrMode()
+  if (mode === 'http') {
+    return await callOcrViaHttp(action, payload, { timeoutMs })
+  }
+  // subprocess mode
   const response = await runOcrCommand('request', {
     timeoutMs,
     input: JSON.stringify({
@@ -45,6 +120,8 @@ async function callOcrRequest(action, payload, { timeoutMs = DEFAULT_TIMEOUT_MS
   return response
 }
 
+// ── Subprocess Mode ───────────────────────────────────────────────────────────
+
 async function runOcrCommand(command, { timeoutMs = DEFAULT_TIMEOUT_MS, input = '' } = {}) {
   const projectRoot = resolveOcrProjectRoot()
   const workerCommand = resolveWorkerCommand(projectRoot)