Add sorting options to the leaderboard (most matched vs. most missing)

[Muskankr]

Let users toggle between viewing "most commonly matched skills" and "most commonly missing skills" for the selected track.

Acceptance criteria:
Toggle/tab control to switch sort mode
Backend supports both orderings (or frontend sorts client-side if the full dataset is already returned)
Selected mode persists while switching career tracks

[Ayush-0918]

I would like to work on this issue. Please assign to me.