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/fix_alembic_version.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python3
+"""Fix alembic version in database"""
+
+from sqlalchemy import create_engine, text
+from app.core.config import settings
+
+# Create database connection
+engine = create_engine(settings.database_url)
+
+with engine.connect() as conn:
+    # Delete the problematic version
+    conn.execute(text("DELETE FROM alembic_version WHERE version_num = '3ede847231ff'"))
+    conn.commit()
+    print("✓ Removed problematic alembic version")
+
+    # Check current version
+    result = conn.execute(text("SELECT version_num FROM alembic_version"))
+    versions = result.fetchall()
+
+    if versions:
+        print(f"Current version(s): {[v[0] for v in versions]}")
+    else:
+        print("No alembic version found in database")
+        # Set to the base version before our new migrations
+        conn.execute(text("INSERT INTO alembic_version (version_num) VALUES ('271dc036ea80')"))
+        conn.commit()
+        print("✓ Set alembic version to 271dc036ea80")
+
+print("\nDone!")