Add Top Songs feature and placeholders for other features (Vishal Nair)

[VSHAL17]

This pull request adds the initial implementation for the Spotify project.

Edited main.cpp to include the main menu and function calls.

Created top_songs.cpp and top_songs.h with the implementation for the Top Songs of the Month feature (Vishal’s part).

Added placeholder files for other team members:

song_rec.cpp/h (Saachin – Song Recommendation)

song_desc.cpp/h (Dinesh – Song + Artist Description)

lyrics_quiz.cpp/h (Izaan – Lyrics Quiz)

most_streamed.cpp/h (Most Streamed Song Guess Game)

This sets up the project structure so each member can add their part.