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/pages/SettingsPage.tsx

@@ -4,7 +4,7 @@ import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card'
 import { Button } from '@/components/ui/button'
 import { useToast } from '@/components/ui/toast'
-import { apiClient } from '@/services/api'
+import { apiClientV2 } from '@/services/apiV2'
 import type { ExportRule } from '@/types/apiV2'
 
 export default function SettingsPage() {
@@ -25,12 +25,12 @@ export default function SettingsPage() {
   // Fetch export rules
   const { data: exportRules, isLoading } = useQuery({
     queryKey: ['exportRules'],
-    queryFn: () => apiClient.getExportRules(),
+    queryFn: () => apiClientV2.getExportRules(),
   })
 
   // Create rule mutation
   const createRuleMutation = useMutation({
-    mutationFn: (rule: any) => apiClient.createExportRule(rule),
+    mutationFn: (rule: any) => apiClientV2.createExportRule(rule),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['exportRules'] })
       setIsCreating(false)
@@ -53,7 +53,7 @@ export default function SettingsPage() {
   // Update rule mutation
   const updateRuleMutation = useMutation({
     mutationFn: ({ ruleId, rule }: { ruleId: number; rule: any }) =>
-      apiClient.updateExportRule(ruleId, rule),
+      apiClientV2.updateExportRule(ruleId, rule),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['exportRules'] })
       setEditingRule(null)
@@ -75,7 +75,7 @@ export default function SettingsPage() {
 
   // Delete rule mutation
   const deleteRuleMutation = useMutation({
-    mutationFn: (ruleId: number) => apiClient.deleteExportRule(ruleId),
+    mutationFn: (ruleId: number) => apiClientV2.deleteExportRule(ruleId),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['exportRules'] })
       toast({