new age: adaptivity and working prototype with usability

[gr1shan1a]

This pull request adds support for assigning and editing a custom color for meetings throughout the backend, database, and frontend. It introduces validation for hex color codes, updates the data model and API, and enhances the user interface to allow users to select and visualize meeting colors.

Backend and Data Model Enhancements:

• Added a new color field to the Meeting entity, database schema (meetings table), and related DTOs to store a hex color code for each meeting.
• Updated meeting creation logic in TelegramBotService to assign the default color when a meeting is created via the bot.

Frontend and UI Improvements:

• Added a color picker input to the meeting edit form, allowing users to select a meeting color.
• Updated the frontend logic to validate, normalize, and submit the color field with meeting updates, including user feedback for invalid color input.
• Implemented utility functions to apply meeting colors to UI elements, ensuring consistent display and fallback to the default color.
• Improved styles for color input and meeting pills for better usability and display, especially on smaller screens.