[Term Entry] Add Cognitive Load

[AnamolR]

Description

This PR adds a new UX psychology and usability concept titled Cognitive Load to the uiux/concepts/ section.

New folder: content/uiux/concepts/cognitive-load/
Markdown file: cognitive-load.md defines cognitive load in UX, describes where it commonly appears in digital interfaces, breaks down the three types (intrinsic, extraneous, and germane), and provides practical techniques to reduce unnecessary mental effort for users.

This entry supports UX decision-making by connecting cognitive psychology principles with interface design strategies and complements related topics like attention, memory, and task flow optimization.

Type of Change

Adding a new entry

Checklist

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

Issues Solved

Closes #6639

[Sriparno08]

Thanks for contributing to Codecademy Docs, @AnamolR!

This entry looks good for a second round of review. 🚀

[mamtawardhani]

Looks good to be merged! 🚀

[github-actions]

👋 @AnamolR
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