Docs: Capitalize React concepts in Learn section

[Ankitaupadhaya]

Description

• This PR improves consistency in the documentation by capitalizing React-specific concepts where appropriate.

Changes include:

• Updated add-react-to-an-existing-project.md to capitalize React, Hooks, Effects, and Transitions consistently.
• Updated adding-interactivity.md with proper capitalization of React concepts.

Why this change?

• React docs use proper capitalization for framework concepts to make them stand out from general programming terms.
• Ensures readability and consistency across the Learn section.
• Aligns with existing style guidelines and previous discussions.

Checklist

• Capitalization corrected for React concepts in the Learn section.
• Verified local build with yarn dev to confirm formatting renders correctly.
• Changes scoped to docs only (no impact on functionality).

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[github-actions]

Size changes

📦 Next.js Bundle Analysis for react-dev

This analysis was generated by the Next.js Bundle Analysis action. 🤖

This PR introduced no changes to the JavaScript bundle! 🙌

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[Ankitaupadhaya]

Okay!! Excited to contribute more :)