data: add neetcode-150.json for custom study plan

[ravikiranp123]

This PR adds the raw topic and problem-slug mapping data for the NeetCode 150 curriculum to the repository.

Key Changes:

• Created neetcode-150.json containing the exact category breakdowns (e.g., "1-D Dynamic Programming", "Sliding Window") and their associated LeetCode problem slugs.
• This file is designed to be paired directly with the new path property introduced in the Custom Study Plans feature, allowing users to render the full NeetCode 150 tree locally in their sidebar.

[NikkyAmresh]

Thanks, the data itself looks good and rendered correctly in my testing. Since this file only works through the path property from #3, I will hold this until the feedback there is addressed (see #3 (comment)).

One note specific to this PR: the slug neetcode-150 is exactly the kind of name that could also exist as a real plan on LeetCode, which makes the source ambiguity in #3 visible here. Once #3 makes the source explicit (a dropdown for LeetCode vs local JSON in the config UI, and a clear override rule), this data file can go in as is. It would also help to add a short comment or README note documenting the schema (category name mapped to an array of problem slugs) so contributors adding similar files know the expected format.