Code review: matrix layout and export cropping fixes

[Copilot]

Comprehensive review of PR #16 fixes for matrix visualization layout and export issues. All previous review feedback has been addressed through sub-PRs #17-#20.

Verified Fixes

Export cropping (js/utils/export-tools.js)

• Width measurement fallback chain now properly validates rect.width before defaulting to 1
• shrinkToContent condition extracted once, eliminating duplicate boolean coercion
• Removed unnecessary explicit undefined initialization

ResizeObserver memory leak (js/renderers/comparison-renderer.js)

• Observer lifecycle managed via comparison-renderer-store.js with proper disconnect on cleanup
• Switched from observing document.body to matrixContainer for efficient, targeted resize detection
• Magic number 0.92 extracted to MATRIX_FILL_RATIO_THRESHOLD with documented rationale

CSS consistency (css/comparison.css)

• Standardized child combinator spacing: .comparison-matrix-grid > .matrix-cell.empty-cell:first-child

Architecture

The fixes maintain the wrapper/container pattern for adaptive layout:

// ResizeObserver adjusts alignment based on content width vs available space
const fillRatio = availableWidth > 0 ? (containerWidth / availableWidth) : 1;
const shouldAlignLeft = sidebarCollapsed
  ? (containerWidth > availableWidth)
  : ((containerWidth > availableWidth) || (fillRatio < MATRIX_FILL_RATIO_THRESHOLD));

Export strategy detects matrix mode and applies shrink-to-content to avoid capturing centered empty margins.

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