Redesign cluster search as collapsible sidebar

[Copilot]

The previous inline search results box blocked the main content, preventing users from navigating to cluster tabs. Search results displayed in a sticky container that grew large enough to hide all cluster content below.

Changes

Replaced inline search with collapsible left sidebar:

• Toggle button fixed to left edge (200px from top, z-index 1000)
• 350px sidebar slides in/out with CSS transitions (left: -350px → 0)
• Sidebar contains search input, results summary, and scrollable result cards
• Full viewport height with independent scroll

Result display:

• Compact cards: tab name + badge, cluster name, highlighted snippet
• Active state uses inset box-shadow (prevents layout shift)
• Click navigates to cluster tab, sidebar remains open
• Auto-focuses search input on open

Interaction:

• Toggle button, close button (X), ESC key all control sidebar
• Enter key triggers search
• Clear button shown only when results exist

Responsive:

• Desktop: 350px sidebar
• Mobile (<768px): 100% width sidebar

Example Structure

// Before: sticky container inserted after intro section
const searchContainer = document.createElement('div');
searchContainer.className = 'cluster-search-container';
introSection.parentNode.insertBefore(searchContainer, introSection.nextSibling);

// After: fixed sidebar at body start
const sidebar = document.createElement('div');
sidebar.innerHTML = `
  <button class="cluster-search-toggle">...</button>
  <div class="cluster-search-panel">
    <div class="cluster-search-header">...</div>
    <div class="cluster-search-body">...</div>
  </div>
`;
document.body.insertBefore(sidebar, document.body.firstChild);

CSS handles visibility via panel.classList.toggle('open') which transitions left property.

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