🧹 [refactor & optimization] Deep investigation and documentation of NDLOCR-Lite

[chottokun]

🎯 What:

• Conducted an in-depth investigation of the latest NDLOCR-Lite repository (v1.2.3) and the api-ndlocr-lite system.
• Created a comprehensive Markdown technical report at docs/ndlocr_refactoring_and_optimization.md.
• Cleared all linting warnings and code style errors across our codebase (e.g., in streamlit_app.py, test files, etc.) to fully satisfy Ruff checks.

💡 Why:

• Deeply understand the core pipeline components (DEIM detector, XY-Cut, and PARSeq cascades).
• Map out design, performance, and security refactorings implemented locally (Lifespan resource management, defusedxml security, ClientDisconnect protection, thread-pool persistence).
• Identify and document the hard constraints with standard PARSeq ONNX models (static batch size of 1) and propose a clear solution path via dynamic axis re-exporting and INT8 quantization.

✅ Verification:

• All 62 unit, integration, security, and schema tests passed perfectly.
• Ruff checking passed cleanly with 0 warnings/errors.

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PR created automatically by Jules for task 15629959499047982991 started by @chottokun

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