refactor: complete V1 to V2 migration and remove legacy architecture

Remove all V1 architecture components and promote V2 to primary:
- Delete all paddle_ocr_* table models (export, ocr, translation, user)
- Delete legacy routers (auth, export, ocr, translation)
- Delete legacy schemas and services
- Promote user_v2.py to user.py as primary user model
- Update all imports and dependencies to use V2 models only
- Update main.py version to 2.0.0

Database changes:
- Fix SQLAlchemy reserved word: rename audit_log.metadata to extra_data
- Add migration to drop all paddle_ocr_* tables
- Update alembic env to only import V2 models

Frontend fixes:
- Fix Select component exports in TaskHistoryPage.tsx
- Update to use simplified Select API with options prop
- Fix AxiosInstance TypeScript import syntax

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

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

frontend/src/pages/TaskHistoryPage.tsx

@@ -28,13 +28,7 @@ import {
   TableHeader,
   TableRow,
 } from '@/components/ui/table'
-import {
-  Select,
-  SelectContent,
-  SelectItem,
-  SelectTrigger,
-  SelectValue,
-} from '@/components/ui/select'
+import { Select } from '@/components/ui/select'
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card'
 
 export default function TaskHistoryPage() {
@@ -296,22 +290,18 @@ export default function TaskHistoryPage() {
               <label className="block text-sm font-medium text-gray-700 mb-2">狀態</label>
               <Select
                 value={statusFilter}
-                onValueChange={(value) => {
-                  setStatusFilter(value as any)
+                onChange={(e) => {
+                  setStatusFilter(e.target.value as any)
                   handleFilterChange()
                 }}
-              >
-                <SelectTrigger>
-                  <SelectValue />
-                </SelectTrigger>
-                <SelectContent>
-                  <SelectItem value="all">全部</SelectItem>
-                  <SelectItem value="pending">待處理</SelectItem>
-                  <SelectItem value="processing">處理中</SelectItem>
-                  <SelectItem value="completed">已完成</SelectItem>
-                  <SelectItem value="failed">失敗</SelectItem>
-                </SelectContent>
-              </Select>
+                options={[
+                  { value: 'all', label: '全部' },
+                  { value: 'pending', label: '待處理' },
+                  { value: 'processing', label: '處理中' },
+                  { value: 'completed', label: '已完成' },
+                  { value: 'failed', label: '失敗' },
+                ]}
+              />
             </div>
 
             <div>

frontend/src/services/apiV2.ts

@@ -8,7 +8,8 @@
  * - Session management
  */
 
-import axios, { AxiosError, AxiosInstance } from 'axios'
+import axios, { AxiosError } from 'axios'
+import type { AxiosInstance } from 'axios'
 import type {
   LoginRequest,
   ApiError,