[Term Entry] UX Research Methods

[AnamolR]

Description

This PR adds a new UX research overview entry titled Research Methods to the uiux/concepts/ section.

New folder: content/uiux/concepts/research-methods/
Markdown file: research-methods.md introduces key UX research techniques, which is a core UX approach that explains when to use different methods during the design process, and outlines both qualitative and quantitative approaches. The entry emphasizes how structured research helps designers make evidence-based decisions and reduce assumptions.

This addition complements related entries such as user interviews, diary studies, card sorting, and usability testing.

Issues Solved

Closes #6604

Type of Change

Adding a new entry

Checklist

• [x] All writings are my own.
• [x] My entry follows the Codecademy Docs style guide.
• [x] My changes generate no new warnings.
• [x] I have performed a self-review of my own writing and code.
• [x] I have checked my entry and corrected any misspellings.
• [x] I have made corresponding changes to the documentation if needed.
• [x] I have confirmed my changes are not being pushed from my forked main branch.
• [x] I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• [x] I have linked any issues that are relevant to this PR in the Issues Solved section.