feat: add frontend support for dual-track processing

- Add ProcessingTrack, ProcessingMetadata types to apiV2.ts
- Add analyzeDocument, getProcessingMetadata, downloadUnified API methods
- Update startTask to support ProcessingOptions
- Update TaskDetailPage with:
  - Processing track badge and description display
  - Enhanced stats grid (pages, text regions, tables, images, confidence)
  - UnifiedDocument download option
  - Translation UI preparation (disabled, awaiting backend)
- Mark Section 7 Frontend Updates as completed in tasks.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/types/apiV2.ts

@@ -44,6 +44,43 @@ export interface SessionInfo {
 
 export type TaskStatus = 'pending' | 'processing' | 'completed' | 'failed'
 
+// ==================== Dual-Track Processing ====================
+
+export type ProcessingTrack = 'ocr' | 'direct' | 'hybrid' | 'auto'
+
+export interface ProcessingMetadata {
+  processing_track: ProcessingTrack
+  processing_time_seconds: number
+  language: string
+  page_count: number
+  total_elements: number
+  total_text_regions: number
+  total_tables: number
+  total_images: number
+  average_confidence: number | null
+  unified_format: boolean
+}
+
+export interface DocumentAnalysisResponse {
+  task_id: string
+  filename: string
+  recommended_track: ProcessingTrack
+  confidence: number
+  reason: string
+  document_info: Record<string, any>
+  is_editable: boolean
+  text_coverage: number | null
+  page_count: number | null
+}
+
+export interface ProcessingOptions {
+  use_dual_track?: boolean
+  force_track?: ProcessingTrack
+  language?: string
+  include_layout?: boolean
+  include_images?: boolean
+}
+
 export interface TaskCreate {
   filename?: string
   file_type?: string
@@ -74,6 +111,9 @@ export interface Task {
   updated_at: string
   completed_at: string | null
   file_deleted: boolean
+  // Dual-track processing fields
+  processing_track?: ProcessingTrack
+  processing_metadata?: ProcessingMetadata
 }
 
 export interface TaskFile {