feat(app): show a compact top-categories summary after scans (#158)

[littfed]

Resolves #158

Summary

Adds a compact top-categories summary card rendered above the detailed expandable result sections. Users immediately see where disk space is consumed without needing to manually expand every section.

Changes

• app/src/App.jsx:
  • Added TopCategoriesSummary({ items, cap = 5 }): groups findings by category using byCategory(), aggregates total reclaimable bytes per category, and displays the top categories ranked by size.
  • Mounted <TopCategoriesSummary items={visibleFindings} /> right above the detailed sections (<DuplicatesSection> and <CategorySection>).
  • Works dynamically for both live preview results and final reports via visibleFindings, and automatically updates if items are quarantined.
• app/src/styles.css:
  • Added compact card styling for .top-categories-summary, list formatting, and monospace values for reclaimable sizes.
• app/src/App.test.mjs & app/src/styles.test.mjs:
  • Added unit test asserting TopCategoriesSummary renders top categories and is placed above detailed sections.
  • Added test validating compact card CSS rules.
• changelog.d/158-top-categories-summary.added.md:
  • Added change fragment describing the feature.

Verification

• npm test in app/ passes 100% (74/74 tests).
• npm run build in app/ builds cleanly.
• python3 scripts/changelog.py check passes cleanly (validated 2 fragments).

[Muawiya-contact]

@LouisDeconinck Can you review it please.

[LouisDeconinck]

Verified against App.jsx — the ranking is correct: byCategory() already sorts groups by total reclaimable bytes descending, so .filter(c => c.total > 0).slice(0, cap) does yield the top categories. f.reclaimable is the right field (same as the existing total at L164), and visibleFindings is memoized and filters quarantined paths, so the summary updates correctly after quarantine and during preview.

One non-blocking nit: aria-label on a plain <div> isn't announced by screen readers without a role — a role="region" or <section> element would make the label effective. Fine to land as-is.

Approved.

[Muawiya-contact]

Thanks for this additional improvement, @littfed! I checked the category ranking, zero-total handling, and filtering after quarantine; the compact summary meets #158, all 12 app test files passed locally, and CI is green. Approved, and thank you @LouisDeconinck for independently checking the aggregation and preview behavior.