feat(ocr): Implement persistent worker pool with SQLite job queue

Major OCR infrastructure improvements:
- Add persistent SQLite-based job queue for OCR tasks
- Implement worker pool with process isolation and auto-restart
- Add OCR engine selector dropdown (Tesseract/PaddleOCR) in upload zone
- Optimize Tesseract preprocessing based on benchmark results (8x faster)
- Add recognize_cif_optimized() with multi-strategy CIF extraction
- Add Romanian CIF checksum validation
- Increase Telegram long polling timeout from 10s to 30s

Squashed commits:
- feat(ocr): Implement persistent worker pool with SQLite job queue
- feat(ocr): Add OCR engine selector dropdown to upload zone
- perf(telegram): Increase long polling timeout from 10s to 30s
- perf(ocr): Optimize Tesseract preprocessing based on benchmark results

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

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

backend/modules/data_entry/services/ocr/__init__.py

@@ -0,0 +1,42 @@
+"""
+OCR Services Module
+
+Provides persistent OCR worker pool with job queue for efficient processing.
+
+Components:
+- ocr_worker_pool: Manages ProcessPoolExecutor with persistent PaddleOCR
+- job_queue: SQLite-based job queue for async processing
+- job_worker: Background task that processes queued jobs
+- tesseract_engine: Optimized Tesseract with multi-PSM and polarity fix
+
+Architecture:
+    FastAPI → job_queue.create_job() → SQLite
+                                          ↓
+    job_worker loop → ocr_worker_pool.submit_task() → Worker Process
+                                                          ↓
+                                                    PaddleOCR/Tesseract
+"""
+
+from .ocr_worker_pool import ocr_worker_pool, OCRWorkerPool
+from .job_queue import job_queue, OCRJobQueue, OCRJob, OCRJobStatus
+from .job_worker import start_job_worker, stop_job_worker
+from .tesseract_engine import TesseractEngine
+from .validation import OCRValidationEngine
+
+__all__ = [
+    # Worker pool
+    "ocr_worker_pool",
+    "OCRWorkerPool",
+    # Job queue
+    "job_queue",
+    "OCRJobQueue",
+    "OCRJob",
+    "OCRJobStatus",
+    # Job worker
+    "start_job_worker",
+    "stop_job_worker",
+    # Engines
+    "TesseractEngine",
+    # Validation
+    "OCRValidationEngine",
+]