Reorganize Flask app files into flask_app folder

[Doriandarko]

Related to #48

Rearranges the Flask app files into a dedicated flask_app folder and updates the README.md with new instructions for running the Flask app.

• File Structure Changes: Moves app.py, requirements.txt, static/css/style.css, templates/base.html, and templates/index.html into a newly created flask_app folder. This reorganization aligns with the goal of having all Flask app-related files in a single directory for better project structure and management.
• README.md Update: Modifies the instructions for running the Flask app to reflect the new file locations within the flask_app folder. This ensures users are correctly guided on how to start the Flask server after the reorganization.

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[Saliiiiiikian]

how to fix it? thanks :) AttributeError: partially initialized module 'typing' has no attribute 'TYPE_CHECKING' (most likely due to a circular import)