feat(ocr): Add docTR OCR engine with metrics infrastructure

Add docTR as primary OCR engine with 2-tier sequential processing,
OCR metrics tracking, and simplified engine selection.

Features:
- docTR OCR engine with light+medium preprocessing tiers
- doctr_plus mode with early exit optimization (~65% fast path)
- OCR metrics dashboard with per-engine statistics
- User OCR preference persistence
- Parallel worker pool for OCR processing
- Cross-validation for extraction quality

Engine options: tesseract, doctr, doctr_plus (recommended), paddleocr

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/router/index.js

@@ -78,6 +78,12 @@ const routes = [
         name: 'ReceiptEdit',
         component: () => import('@data-entry/views/receipts/ReceiptCreateView.vue'),
         meta: { requiresAuth: true, title: 'Editare Bon - ROA2WEB' }
+      },
+      {
+        path: 'ocr-metrics',
+        name: 'OCRMetrics',
+        component: () => import('@data-entry/views/OCRMetricsView.vue'),
+        meta: { requiresAuth: true, title: 'Metrici OCR - ROA2WEB' }
       }
     ]
   },