feat: enhance Mind Map into study planner with academic tracking system

[bansalrujul07]

📌 Description

This PR improves the existing Mind Map feature in StudyMatePlus by transforming it from a generic diagram editor into a more student-focused study planning tool. Previously, the Mind Map only acted as a visual node editor without any academic structure. This update introduces study-oriented metadata to each node so students can better organize and track their syllabus. Now each node can represent real study components like subjects, units, topics, and subtopics along with progress tracking and priority levels. The goal is to make the Mind Map more useful for exam preparation, revision planning, and syllabus tracking while keeping the UI and overall structure unchanged.

🔗 Related Issue

Closes #132

🛠 Changes Made

1. Extended Mind Map nodes to support study-focused metadata:

• Study Level (Subject / Unit / Topic / Subtopic)
• Progress Status (Not Started / In Progress / Revised / Completed)
• Priority Level (High / Medium / Low)

2. Updated node UI to visually display:

• Subject badge
• Progress status badge
• Priority indicator
• Study level label

3. Enhanced Inspector panel:

• Added dropdowns for Study Level, Progress, and Priority
• Improved layout order for better usability

4. Improved node creation logic:
   -- Default values added for new nodes:

• Study Level: Topic
• Progress: Not Started
• Priority: Medium
  -- Ensures consistent structure across all node types

5. Ensured backward compatibility:

• Existing nodes still work without breaking changes
• No modification to backend or database structure

✅ Checklist

• Code runs locally
• Followed project structure
• No console errors
• Properly tested changes
• Linked the issue

🚀 Notes for Reviewers

• This PR is intentionally kept minimal to avoid breaking existing Mind Map functionality.
• Changes are mainly additive (no major refactor).
• UI structure remains unchanged to preserve consistency with current app design.
• Focus is on enhancing usability for students without increasing complexity.

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