refactor: remove unused code and migrate legacy API

Backend cleanup:
- Remove ocr_service_original.py (legacy OCR service, replaced by ocr_service.py)
- Remove preprocessor.py (unused, functionality absorbed by layout_preprocessing_service.py)
- Remove pdf_font_manager.py (unused, never referenced by any service)

Frontend cleanup:
- Remove MarkdownPreview.tsx (unused component)
- Remove ResultsTable.tsx (unused, replaced by TaskHistoryPage)
- Remove services/api.ts (legacy API client, migrated to apiV2)
- Remove types/api.ts (legacy types, migrated to apiV2.ts)

API migration:
- Add export rules CRUD methods to apiClientV2
- Update SettingsPage.tsx to use apiClientV2
- Update Layout.tsx to use only apiClientV2 for logout

This reduces ~1,500 lines of redundant code and unifies the API client.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/services/apiV2.ts

@@ -38,6 +38,7 @@ import type {
   TranslationStatusResponse,
   TranslationListResponse,
   TranslationResult,
+  ExportRule,
 } from '@/types/apiV2'
 
 /**
@@ -713,6 +714,39 @@ class ApiClientV2 {
     link.click()
     window.URL.revokeObjectURL(link.href)
   }
+
+  // ==================== Export Rules APIs ====================
+
+  /**
+   * Get export rules
+   */
+  async getExportRules(): Promise<ExportRule[]> {
+    const response = await this.client.get<ExportRule[]>('/export/rules')
+    return response.data
+  }
+
+  /**
+   * Create export rule
+   */
+  async createExportRule(rule: Omit<ExportRule, 'id' | 'created_at'>): Promise<ExportRule> {
+    const response = await this.client.post<ExportRule>('/export/rules', rule)
+    return response.data
+  }
+
+  /**
+   * Update export rule
+   */
+  async updateExportRule(ruleId: number, rule: Partial<ExportRule>): Promise<ExportRule> {
+    const response = await this.client.put<ExportRule>(`/export/rules/${ruleId}`, rule)
+    return response.data
+  }
+
+  /**
+   * Delete export rule
+   */
+  async deleteExportRule(ruleId: number): Promise<void> {
+    await this.client.delete(`/export/rules/${ruleId}`)
+  }
 }
 
 // Export singleton instance