feat: add backend OCR manual proxy endpoint (refs #135)

Add POST /api/ocr/extract/manual endpoint that proxies to the Python
OCR service's manual extraction pipeline. Includes Pro tier gating via
document.scanMaintenanceSchedule, PDF-only validation, 200MB file size
limit, and async 202 job response for polling via existing job status
endpoint.

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

backend/src/features/ocr/domain/ocr.service.ts

@@ -5,6 +5,8 @@ import { logger } from '../../../core/logging/logger';
 import { ocrClient, JobNotFoundError } from '../external/ocr-client';
 import type {
   JobResponse,
+  ManualJobResponse,
+  ManualJobSubmitRequest,
   OcrExtractRequest,
   OcrJobSubmitRequest,
   OcrResponse,
@@ -278,6 +280,66 @@ export class OcrService {
     }
   }
 
+  /**
+   * Submit an async manual extraction job for PDF owner's manuals.
+   *
+   * @param userId - User ID for logging
+   * @param request - Manual job submission request
+   * @returns Manual job response with job ID
+   */
+  async submitManualJob(userId: string, request: ManualJobSubmitRequest): Promise<ManualJobResponse> {
+    // Validate file size for async processing (200MB max)
+    if (request.fileBuffer.length > MAX_ASYNC_SIZE) {
+      const err: any = new Error(
+        `File too large. Max: ${MAX_ASYNC_SIZE / (1024 * 1024)}MB.`
+      );
+      err.statusCode = 413;
+      throw err;
+    }
+
+    // Manual extraction only supports PDF
+    if (request.contentType !== 'application/pdf') {
+      const err: any = new Error(
+        `Unsupported file type: ${request.contentType}. Manual extraction requires PDF files.`
+      );
+      err.statusCode = 400;
+      throw err;
+    }
+
+    logger.info('Manual job submit requested', {
+      operation: 'ocr.service.submitManualJob',
+      userId,
+      contentType: request.contentType,
+      fileSize: request.fileBuffer.length,
+      hasVehicleId: !!request.vehicleId,
+    });
+
+    try {
+      const result = await ocrClient.submitManualJob(
+        request.fileBuffer,
+        request.contentType,
+        request.vehicleId
+      );
+
+      logger.info('Manual job submitted', {
+        operation: 'ocr.service.submitManualJob.success',
+        userId,
+        jobId: result.jobId,
+        status: result.status,
+        estimatedSeconds: result.estimatedSeconds,
+      });
+
+      return result;
+    } catch (error) {
+      logger.error('Manual job submit failed', {
+        operation: 'ocr.service.submitManualJob.error',
+        userId,
+        error: error instanceof Error ? error.message : 'Unknown error',
+      });
+      throw error;
+    }
+  }
+
   /**
    * Get the status of an async OCR job.
    *