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/telegram/bot_main.py

@@ -260,7 +260,11 @@ async def main():
         logger.info("🤖 Starting Telegram bot polling...")
         await telegram_app.initialize()
         await telegram_app.start()
-        await telegram_app.updater.start_polling(drop_pending_updates=True)
+        await telegram_app.updater.start_polling(
+            drop_pending_updates=True,
+            poll_interval=0,        # No delay between polls
+            timeout=30              # Long poll timeout 30 seconds (reduces requests from ~6/min to ~2/min)
+        )
 
         logger.info("✅ Telegram bot is now running and polling for updates")
         logger.info(f"📱 Bot ready to receive messages at @{(await telegram_app.bot.get_me()).username}")