fix: resolve all lint errors across source and test files

- Fix unused function parameters (prefix with _)
- Fix unused imports in test files
- Fix import ordering in test files
- Auto-fix formatting issues across 22 files

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/components/CandidateCard.tsx

@@ -34,7 +34,7 @@ export function CandidateCard({
 	priceCents,
 	categoryName,
 	categoryIcon,
-	imageFilename,
+	imageFilename: _imageFilename,
 	imageUrl,
 	productUrl,
 	threadId,