feat: Complete Subject Management System with Validation and Sub-Details (#412)

[Parmarprashant]

Summary

This PR transforms the basic "Subjects" section into a fully functional learning management layer. It introduces robust management features (CRUD), strict input validation, and an expandable detail view for tracking topics, resources, and notes per subject.

Key Enhancements

• Full Subject CRUD :
  • Edit : Users can now rename subjects and change their associated colors.
  • Delete : Subjects can be removed, with a cascade effect that cleans up associated tasks and resources.
• Subject Detail View (Learning Containers) :
  • Each subject now acts as a container that can be expanded into a dedicated modal.
  • Users can add Topics , Resource Links , and Notes specifically for that subject.
  • Topics include completion tracking (checkboxes) to monitor study progress at a granular level.
• Data Integrity & Validation :
  • Duplicate Prevention : Both frontend and backend now block the creation of duplicate subject names (case-insensitive).
  • Input Sanitization : Minimum length requirements (2+ characters) and trimming ensure high-quality data.
  • Relational Integrity : New subject_details table in database.js linked via foreign keys.
• Improved UI/UX :
  • Hover actions in the sidebar for quick editing/deletion.
  • Modal-based detail management for a focused workflow.
  • Dynamic badge updates reflecting only pending tasks per subject.

Technical Changes

• Backend : Added API endpoints in server.js for subject updates, deletions, and detail management.
• Store : Expanded store.js with async methods to handle the new subject-specific data operations.
• Frontend : Updated app.js to handle the new modal interactions and sidebar event listeners.

Verification Results

• Duplicate subjects are blocked with a user-friendly alert.
• Subject name edits reflect immediately across the app (Sidebar and Tasks).
• Deleting a subject successfully removes all its linked tasks and resources.
• Topics added to a subject are saved correctly and can be toggled as completed.

Fixes

Fixes #412