docs: add JavaScript interview FAQs (basic + advanced)

[KL2400040448]

Adds two FAQ files under javascript-interview-questions/:

• basic.md — 10 concise, common JS interview questions and answers.
• advanced.md — 10 advanced topics (Node, streams, memory profiling, security, concurrency).

Why:

• Helps contributors and interview candidates prepare quickly.
• Keeps basic and advanced topics separated for organization.

What to review:

• Accuracy and clarity of short answers.
• Suggestions for adding code snippets or references (I can add examples in follow-ups).

Closes: #317