Reorganize documentation sidebar for better UX (#4692)

[ProblemShooter]

Summary

This PR reorganizes the documentation sidebar to improve navigation and user experience.

Changes

• Group content into logical categories with emoji indicators for visual distinction
• Add section captions:
  • 🧪 Getting Started
  • 🎯 Hosting a Challenge
  • 🚀 Participating in Challenges
  • ⚙️ Developer Guide
  • 📖 Examples & Tutorials
  • 🛠️ Troubleshooting
  • 📚 Reference
• Improve navigation structure and user experience
• Maintain maxdepth at 2 for all sections to ensure consistent documentation depth

Related Issue

Fixes #4692

Benefits

• Clearer organization of documentation content
• Better user experience with visual indicators
• Easier navigation for both new and existing users
• More intuitive grouping of related documentation pages

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 91.87%. Comparing base (e9e38e9) to head (0a2c994).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4800   +/-   ##
=======================================
  Coverage   91.87%   91.87%           
=======================================
  Files          85       85           
  Lines        7105     7105           
=======================================
  Hits         6528     6528           
  Misses        577      577           

Flag	Coverage Δ
backend	96.66% <ø> (ø)
frontend	87.14% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
Accounts & Authentication	100.00% <ø> (ø)
Challenges Management	95.34% <ø> (ø)
Job Processing	98.19% <ø> (ø)
Participants & Teams	100.00% <ø> (ø)
Challenge Hosts	100.00% <ø> (ø)
Analytics	100.00% <ø> (ø)
Web Interface	100.00% <ø> (ø)
Frontend (Gulp)	87.14% <ø> (ø)
All Models	97.58% <ø> (ø)
All Views	100.00% <ø> (ø)
All Serializers	98.82% <ø> (ø)
Utility Functions	96.79% <ø> (ø)
Core Configuration	82.35% <ø> (ø)

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