chore(lint): enable strict ESLint rules and fix unused-vars violations (F4.1)

Enable no-console (warn, allow error), @typescript-eslint/no-unused-vars
(warn, ignore _ prefix), and @typescript-eslint/no-explicit-any (warn).
Fix all 26 no-unused-vars violations across 9 files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/shared/utils/documentDisplayUtils.ts

@@ -6,7 +6,7 @@
  */
 
 import { getFileIcon } from '~/utils/fileIcons'
-import { canPreviewDocument, isImageDocument, isPdfDocument } from '~/utils/documentPreview'
+import { isImageDocument, isPdfDocument } from '~/utils/documentPreview'
 
 export const PDF_PREVIEW_MAX_BYTES = 5 * 1024 * 1024