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/user.py

@@ -1,6 +1,6 @@
 """
-Tool_OCR - User Model
-User authentication and management
+Tool_OCR - User Model v2.0
+External API authentication with simplified schema
 """
 
 from sqlalchemy import Column, Integer, String, DateTime, Boolean
@@ -11,24 +11,39 @@ from app.core.database import Base
 
 
 class User(Base):
-    """User model for JWT authentication"""
+    """
+    User model for external API authentication
 
-    __tablename__ = "paddle_ocr_users"
+    Uses email as primary identifier from Azure AD.
+    No password storage - authentication via external API only.
+    """
 
-    id = Column(Integer, primary_key=True, index=True)
-    username = Column(String(50), unique=True, nullable=False, index=True)
-    email = Column(String(100), unique=True, nullable=False, index=True)
-    password_hash = Column(String(255), nullable=False)
-    full_name = Column(String(100), nullable=True)
-    is_active = Column(Boolean, default=True, nullable=False)
-    is_admin = Column(Boolean, default=False, nullable=False)
+    __tablename__ = "tool_ocr_users"
+
+    id = Column(Integer, primary_key=True, index=True, autoincrement=True)
+    email = Column(String(255), unique=True, nullable=False, index=True,
+                  comment="Primary identifier from Azure AD")
+    display_name = Column(String(255), nullable=True,
+                         comment="Display name from API response")
     created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
-    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False)
+    last_login = Column(DateTime, nullable=True)
+    is_active = Column(Boolean, default=True, nullable=False, index=True)
 
     # Relationships
-    ocr_batches = relationship("OCRBatch", back_populates="user", cascade="all, delete-orphan")
-    export_rules = relationship("ExportRule", back_populates="user", cascade="all, delete-orphan")
-    translation_configs = relationship("TranslationConfig", back_populates="user", cascade="all, delete-orphan")
+    tasks = relationship("Task", back_populates="user", cascade="all, delete-orphan")
+    sessions = relationship("Session", back_populates="user", cascade="all, delete-orphan")
+    audit_logs = relationship("AuditLog", back_populates="user")
 
     def __repr__(self):
-        return f"<User(id={self.id}, username='{self.username}', email='{self.email}')>"
+        return f"<User(id={self.id}, email='{self.email}', display_name='{self.display_name}')>"
+
+    def to_dict(self):
+        """Convert user to dictionary"""
+        return {
+            "id": self.id,
+            "email": self.email,
+            "display_name": self.display_name,
+            "created_at": self.created_at.isoformat() if self.created_at else None,
+            "last_login": self.last_login.isoformat() if self.last_login else None,
+            "is_active": self.is_active
+        }