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/models/__init__.py

@@ -1,31 +1,20 @@
 """
-Tool_OCR - Database Models
+Tool_OCR - Database Models (V2)
 
-New schema with external API authentication and user task isolation.
+External API authentication with user task isolation.
 All tables use 'tool_ocr_' prefix for namespace separation.
 """
 
-# New models for external authentication system
-from app.models.user_v2 import User
+from app.models.user import User
 from app.models.task import Task, TaskFile, TaskStatus
 from app.models.session import Session
-
-# Legacy models (will be deprecated after migration)
-from app.models.ocr import OCRBatch, OCRFile, OCRResult
-from app.models.export import ExportRule
-from app.models.translation import TranslationConfig
+from app.models.audit_log import AuditLog
 
 __all__ = [
-    # New authentication and task models
     "User",
     "Task",
     "TaskFile",
     "TaskStatus",
     "Session",
-    # Legacy models (deprecated)
-    "OCRBatch",
-    "OCRFile",
-    "OCRResult",
-    "ExportRule",
-    "TranslationConfig",
+    "AuditLog",
 ]