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>

backend/app/routers/admin.py

@@ -10,8 +10,8 @@ from datetime import datetime
 from fastapi import APIRouter, Depends, HTTPException, status, Query
 from sqlalchemy.orm import Session
 
-from app.core.deps import get_db, get_current_admin_user_v2
-from app.models.user_v2 import User
+from app.core.deps import get_db, get_current_admin_user
+from app.models.user import User
 from app.services.admin_service import admin_service
 from app.services.audit_service import audit_service
 
@@ -23,7 +23,7 @@ router = APIRouter(prefix="/api/v2/admin", tags=["Admin"])
 @router.get("/stats", summary="Get system statistics")
 async def get_system_stats(
     db: Session = Depends(get_db),
-    admin_user: User = Depends(get_current_admin_user_v2)
+    admin_user: User = Depends(get_current_admin_user)
 ):
     """
     Get overall system statistics
@@ -47,7 +47,7 @@ async def list_users(
     page: int = Query(1, ge=1),
     page_size: int = Query(50, ge=1, le=100),
     db: Session = Depends(get_db),
-    admin_user: User = Depends(get_current_admin_user_v2)
+    admin_user: User = Depends(get_current_admin_user)
 ):
     """
     Get list of all users with statistics
@@ -79,7 +79,7 @@ async def get_top_users(
     metric: str = Query("tasks", regex="^(tasks|completed_tasks)$"),
     limit: int = Query(10, ge=1, le=50),
     db: Session = Depends(get_db),
-    admin_user: User = Depends(get_current_admin_user_v2)
+    admin_user: User = Depends(get_current_admin_user)
 ):
     """
     Get top users by metric
@@ -115,7 +115,7 @@ async def get_audit_logs(
     page: int = Query(1, ge=1),
     page_size: int = Query(100, ge=1, le=500),
     db: Session = Depends(get_db),
-    admin_user: User = Depends(get_current_admin_user_v2)
+    admin_user: User = Depends(get_current_admin_user)
 ):
     """
     Get audit logs with filtering
@@ -169,7 +169,7 @@ async def get_user_activity_summary(
     user_id: int,
     days: int = Query(30, ge=1, le=365),
     db: Session = Depends(get_db),
-    admin_user: User = Depends(get_current_admin_user_v2)
+    admin_user: User = Depends(get_current_admin_user)
 ):
     """
     Get user activity summary for the last N days