Merge main into upgrade branch and add missing pill element styles

[Copilot]

Resolved merge conflicts between the upgrade branch and main while preserving enhancements to the matrix chain DP visualization (Godbolt links, Overload article reference).

Changes

• Merge resolution: Kept enhanced HTML structure with external resource links over simpler main branch version
• Missing styles: Added CSS for .pill, .pill-row, .title-row elements that were referenced in HTML but had no corresponding styles

.pill {
    display: inline-flex;
    padding: 6px 14px;
    border-radius: 999px;
    background: rgba(0, 217, 255, 0.12);
    border: 1px solid rgba(0, 217, 255, 0.35);
}

Technical notes

CSS indentation follows existing codebase convention (visual nesting for related selectors, though not functionally significant in plain CSS).

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