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/check_tables.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+"""Check existing tables"""
+
+from sqlalchemy import create_engine, text
+from app.core.config import settings
+
+engine = create_engine(settings.database_url)
+
+with engine.connect() as conn:
+    # Get all tables
+    result = conn.execute(text("SHOW TABLES"))
+    tables = [row[0] for row in result.fetchall()]
+
+    print("Existing tables:")
+    for table in sorted(tables):
+        print(f"  - {table}")
+
+    # Check which V2 tables exist
+    v2_tables = ['tool_ocr_users', 'tool_ocr_sessions', 'tool_ocr_tasks',
+                 'tool_ocr_task_files', 'tool_ocr_audit_logs']
+    print("\nV2 Tables status:")
+    for table in v2_tables:
+        exists = table in tables
+        print(f"  {'✓' if exists else '✗'} {table}")
+
+    # Check which old tables exist
+    old_tables = ['paddle_ocr_users', 'paddle_ocr_batches', 'paddle_ocr_files',
+                  'paddle_ocr_results', 'paddle_ocr_export_rules', 'paddle_ocr_translation_configs']
+    print("\nOld Tables status:")
+    for table in old_tables:
+        exists = table in tables
+        print(f"  {'✓' if exists else '✗'} {table}")