feat: add receipt proxy tier guard, 422 forwarding, and tests (refs #139)

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

backend/src/features/ocr/api/ocr.routes.ts

@@ -2,6 +2,7 @@
  * @ai-summary Fastify routes for OCR API
  */
 import { FastifyInstance, FastifyPluginAsync, FastifyPluginOptions } from 'fastify';
+import { requireTier } from '../../../core/middleware/require-tier';
 import { OcrController } from './ocr.controller';
 
 export const ocrRoutes: FastifyPluginAsync = async (
@@ -23,9 +24,9 @@ export const ocrRoutes: FastifyPluginAsync = async (
     handler: ctrl.extractVin.bind(ctrl),
   });
 
-  // POST /api/ocr/extract/receipt - Receipt-specific OCR extraction
+  // POST /api/ocr/extract/receipt - Receipt-specific OCR extraction (Pro tier required)
   fastify.post('/ocr/extract/receipt', {
-    preHandler: [requireAuth],
+    preHandler: [requireAuth, requireTier('fuelLog.receiptScan')],
     handler: ctrl.extractReceipt.bind(ctrl),
   });