Enable ESLint no-case-declarations rule (#4348)

# Description of Changes
Enable ESLint [no-case-declarations
rule](https://eslint.org/docs/latest/rules/no-case-declarations)

frontend/src/services/enhancedPDFProcessingService.ts

@@ -459,11 +459,12 @@ export class EnhancedPDFProcessingService {
       case 'failed':
         this.metrics.failedFiles++;
         break;
-      case 'cacheHit':
+      case 'cacheHit': {
         // Update cache hit rate
         const totalAttempts = this.metrics.totalFiles + 1;
         this.metrics.cacheHitRate = (this.metrics.cacheHitRate * this.metrics.totalFiles + 1) / totalAttempts;
         break;
+      }
     }
   }
 

frontend/src/services/fileAnalyzer.ts

@@ -148,15 +148,17 @@ export class FileAnalyzer {
       case 'immediate_full':
         return pageCount * baseTime;
 
-      case 'priority_pages':
+      case 'priority_pages': {
         // Estimate time for priority pages (first 10)
         const priorityPages = Math.min(pageCount, 10);
         return priorityPages * baseTime;
+      }
 
-      case 'progressive_chunked':
+      case 'progressive_chunked': {
         // Estimate time for first chunk (20 pages)
         const firstChunk = Math.min(pageCount, 20);
         return firstChunk * baseTime;
+      }
 
       default:
         return pageCount * baseTime;