UI and Save Management improvements

[JaviLendi]

This pull request introduces several improvements and new features to the VLM application, focusing on enhanced state management, UI/UX upgrades, and expanded aerodynamic configuration support. The most significant changes include improved state saving/loading with timestamping, a modernized and responsive language selector, new settings and info pop-up UI components, and updates to aerodynamic configuration files to support additional stabilizer definitions.

Backend functionality and state management:

• Added timestamped state saving after VLM computation, ensuring unique state files for each result and improving session management.
• Updated the VLM state loading endpoint to accept file uploads, providing more robust error handling and returning updated aerodynamic metrics after state restoration.
• Introduced datetime import for timestamping purposes.
• Commented out legacy session state saving logic to avoid overwriting states and prepare for the new approach.

Aerodynamic configuration updates:

• Updated cache_plane_variables.txt and src/vlm/data/cache_plane_variables.txt to support definitions for horizontal_stabilizer and vertical_stabilizer, enabling more comprehensive aircraft modeling. [1] [2]

UI/UX improvements (CSS):

• Implemented an info pop-up component for contextual help, complete with smooth animations and close button styling.
• Refined button styles for better interactivity, including hover effects, transitions, and consistent sizing. [1] [2]

General updates:

• Updated Python notebook version metadata for compatibility.
• Minor CSS refactoring for clarity, including renaming and reorganizing comments for navigation and hero sections. [1] [2] [3]

These changes collectively improve both the backend robustness and the frontend user experience, making the application more reliable, flexible, and user-friendly.