Modularize application: planning and architecture (Flask Blueprints)

[justogm]

We need to modularize the app to improve maintainability and scalability, using Flask Blueprints for each major component. This issue will serve as the parent tracking issue for the modularization effort.

Goals

• Define main modules/components as Flask Blueprints
• Plan interfaces and dependencies
• Track progress on sub-tasks

Sub-issues to be created:

• Extract UI components to a blueprint
• Separate gaze tracking logic into
• Isolate data storage and state management as a blueprint
• Modularize API integration into a blueprint
• Update documentation to reflect modular & blueprint-based structure

This issue will be updated as sub-issues are created and progress is made.