[Naomi's Sprint] Add Section Headers to Long Lessons

Following up on https://github.com/freeCodeCamp/freeCodeCamp/issues/69286, the 83 lectures below need section headers to break up long blocks of prose and make them easier to scan.

Tick each lecture off as its section headers are added. Each checkbox links to the lecture, with a source link identifying the exact file.

Acceptance Criteria

• Add short, Title Case ## section headers before each major subtopic in the lecture body (# --description-- or # --interactive--, as used by the file).
• Follow the natural structure of the content without rewriting the existing prose.
• Use How Does the Sort Method Work? as the heading example.
• Preserve the front matter, code blocks, and # --questions-- section unchanged.
• Ensure each lecture still reads clearly from beginning to end.

responsive-web-design-v9

• What Are Accessibility Concerns Around Using Animations, and How Can prefers-reduced-motion Help? (source)
• What Are Some Common File Types You Will Work With in Web Applications? (source)
• What Are Some Default Browser Styles Applied to HTML? (source)
• What Are the Accessibility Benefits for Good Link Text, and What Are Examples of Good Link Text? (source)
• What Are the Basic Parts of a Computer? (source)
• What Are the Fundamentals of Typography? (source)
• What Is Color Theory in Design? (source)
• What Is the @font-face At-Rule, and How Does It Work? (source)
• What Is the CSS Filter Property, and What Are Common Examples? (source)
• What Is the Difference Between Absolute and Relative Paths? (source)

javascript-v9

• How Can You Match and Replace All Occurrences in a String? (source)
• How Do Event Bubbling, and Event Delegation Work? (source)
• How Does the Submit Event Work with Forms? (source)
• What Are Cookies, and How Do They Work? (source)
• What Are Sets in JavaScript, and How Does It Differ from WeakSets? (source)
• What Are Some Examples of Using Advanced JavaScript Debugging Techniques? (source)
• What Is Asynchronous JavaScript, and How Does It Differ from Synchronous JavaScript? (source)
• What Is Binary Search and How Does It Differ From Linear Search? (source)
• What Is the Math Object in JavaScript, and What Are Some Common Methods? (source)

front-end-development-libraries-v9

• How Can You Create Custom Hooks in React? (source)
• How Can You Debug Your React Components Using the React DevTools? (source)
• How Do Default and Named Exports Work in React Components? (source)
• How Do You Pass Props from a Parent Component to a Child Component in React? (source)
• How Do You Render Lists in React? (source)
• How Does Data Fetching Work in React? (source)
• What Are Components in React, and How Do They Work? (source)
• What Are React Server Components, and How Do They Work? (source)
• What Are State Management Libraries, and When Should You Use Them? (source)
• What Is Dependency Management, and How Does It Work with Libraries Like React? (source)
• What Is Security Testing? (source)
• What Is Type Narrowing, and How Does It Work? (source)
• What Is Vite, and How Can It Be Used to Set Up a New React Project? (source)
• What Is a CSS Framework, and What Are Some Advantages and Disadvantages of Using It? (source)
• What Is the Difference Between Real Performance and Perceived Performance? (source)
• What Is the useActionState Hook, and How Does It Work? (source)
• What Is the useOptimistic Hook, and How Does It Work? (source)

python-v9

• How Do Classes Work and How Do They Differ From Objects? (source)
• How Do Conditional Statements and Logical Operators Work? (source)
• How Do Loops Work? (source)
• How Do You Install, Configure and Use Python in Your Local Environment? (source)
• How to Handle Object Attributes Dynamically? (source)
• What Are List Comprehensions and What Are Some Useful Functions to Work With Lists? (source)
• What Are Lists and How Do They Work? (source)
• What Are Sets, and How Do They Work? (source)
• What Are Some Common Methods Used for Lists? (source)
• What Are Special Methods and What Are They Used For? (source)
• What Is Abstraction and How Does It Help Keep Complex Systems Organized? (source)
• What Is Binary Search and How Does It Differ From Linear Search? ([source](https: