Resolve merge conflicts between Upgrade and main branches

[Copilot]

PR #21 had merge conflicts in index.html and style.css due to divergent styling approaches and the addition of Godbolt links.

Changes

• Merged main's CSS: Adopted main's gradient-based design system with improved spacing, table styling, and color variables
• Preserved Godbolt links: Integrated Compiler Explorer and Runtime comparison links inline within the subtitle
• Added link styling: Applied accent color and hover transitions to subtitle anchors for visual consistency

Result

<p class="subtitle">Interactive Dynamic Programming Visualization | 
    <a href="https://godbolt.org/z/4MenTYK6E" target="_blank">Compiler Explorer ↗</a> | 
    <a href="https://godbolt.org/z/b3x3ao14K" target="_blank">Runtime comparison ↗</a>
</p>

.subtitle a {
    color: var(--accent);
    text-decoration: none;
    transition: color 0.15s ease;
}

Once this PR merges into Upgrade, PR #21 will be clear to merge into main.

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[andyD123]

ok