feat: Add public skills leaderboard page (#383)

[Aryanbuha890]

Summary

Resolves #383. Adds a public "most in-demand skills" leaderboard page that displays anonymized, track-filterable aggregations of matched and missing skills.

Key Changes

• Backend:
  • GET /api/skills-leaderboard/ public endpoint.
  • Django caching layer (5-minute cache expiry) for periodic updates and database security.
  • Aggregation calculation counters.
  • Full test suite in tests.py.
• Frontend:
  • Standalone SkillsLeaderboard visualizer with track switches and gauge progress indicators.
  • Navbar links and react-router-dom route config.

[vercel]

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[Muskankr]

@Aryanbuha890 , Resolve CI failing

[Aryanbuha890]

@Aryanbuha890 , Resolve CI failing

@Muskankr Please check it now.

[Muskankr]

@Aryanbuha890 , Resolve merge conflicts

[Aryanbuha890]

@Aryanbuha890 , Resolve merge conflicts

@Muskankr Please check it.