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/components/Layout.tsx

@@ -1,7 +1,6 @@
 import { Outlet, NavLink, useNavigate } from 'react-router-dom'
 import { useTranslation } from 'react-i18next'
 import { useAuthStore } from '@/store/authStore'
-import { apiClient } from '@/services/api'
 import { apiClientV2 } from '@/services/apiV2'
 import {
   Upload,
@@ -29,12 +28,7 @@ export default function Layout() {
 
   const handleLogout = async () => {
     try {
-      // Use V2 API if authenticated with V2
-      if (apiClientV2.isAuthenticated()) {
-        await apiClientV2.logout()
-      } else {
-        apiClient.logout()
-      }
+      await apiClientV2.logout()
     } catch (error) {
       console.error('Logout error:', error)
     } finally {