feat: improve StudyPlan UI and user experience

[aman-UI2006]

Related Issue

Closes #471

Summary

This PR improves the overall StudyPlan UI, frontend structure, responsiveness, and user experience. The update modernizes the interface with cleaner styling, improved layout consistency, enhanced interactions, and better maintainability while preserving existing functionality.

Changes Made

• Improved overall UI consistency and visual hierarchy
• Enhanced navbar, dashboard, cards, buttons, and modal styling
• Added cleaner spacing, typography, and responsive layouts
• Refactored CSS structure into modular sections for maintainability
• Improved dark mode and theme consistency
• Added smoother transitions and micro-interactions
• Improved form structure and user feedback experience
• Fixed minor UI/UX inconsistencies and readability issues
• Added accessibility improvements including focus visibility and reduced motion support
• Improved JavaScript structure and reusable utility organization
• Enhanced sidebar navigation and interactive elements
• Updated project structure documentation in README

Testing

Tested locally by running the application with:

npm start

Verified:

• Navbar and sidebar navigation
• Dashboard layout and responsiveness
• Modal open/close interactions
• Calendar/task-related interactions
• Smart Paste functionality
• Focus mode behavior
• Settings and theme toggles
• Responsive layouts on mobile/tablet widths
• Toast notifications and interaction feedback
• No console or runtime errors during usage

Screenshots

Dashboard UI

Additional UI Improvements

Tasks / Focus Mode

Calendar / Planner View

Checklist

• Code follows project style
• Tested locally
• No unrelated changes included
• Documentation updated (if applicable)