[FEATURE] Add computer science fundamental notes and problems

[coding-nb]

Feature Description

Add CN, DBMS , COA notes and problems

Problem It Solves

CS Fundamentals are most asked Q's in interviews.

Additional Context

Add references, screenshots, or examples if needed.

[NamanBharsakale]

hi @pushkarscripts ,

I have already explored and understood the project structure and I noticed that the website can be improved by adding Computer Science fundamentals content/resources in a structured way. I’m interested in contributing to this feature and can work on both the content organization and implementation.

Please assign this issue to me under GSSoC'26. Thank you!