feat(search): add categorized search results presentation (#132)

[Dyu20705]

Issue relationships

Parent issue: #128
Depends on: #131 (PR #154 merged)
Completes: Epic #128

Problem and scope

Implements Issue #132: Categorized Search Results.

• Enhances note list board presentation with contextual categorization during search queries:
  • TITLE MATCHES (notes whose title matches search query)
  • TAG MATCHES (notes matching via tag queries or # prefix)
  • JAPANESE STUDY (notes matching Japanese study templates/vocab/kanji/grammar)
  • CONTENT MATCHES (notes matching body content)
• Preserves canonical searchClient ownership, worker scoring, and inverted index pipelines.
• Preserves standard PINNED and NOTES sections when search query is cleared.
• Preserves 2D keyboard navigation, active selection, and performance budgets.

Verification evidence

npm run test:content     -> PASS (3/3 passed)
npm run lint             -> PASS (0 errors, 0 warnings)
npm run test:unit        -> PASS (290/290 passed)
npm run test:integration -> PASS (107/107 passed)
npm run test:perf        -> PASS (4/4 passed)
git diff --check         -> PASS (clean)

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