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/schemas/translation.py

@@ -1,124 +0,0 @@
-"""
-Tool_OCR - Translation Schemas (RESERVED)
-Request/response models for translation endpoints
-"""
-
-from typing import Optional, Dict, List, Any
-from pydantic import BaseModel, Field
-
-
-class TranslationRequest(BaseModel):
-    """
-    Translation request schema (RESERVED)
-
-    Expected format for document translation requests
-    """
-    file_id: int = Field(..., description="File ID to translate")
-    source_lang: str = Field(..., description="Source language code (zh, en, ja, ko)")
-    target_lang: str = Field(..., description="Target language code (zh, en, ja, ko)")
-    engine_type: Optional[str] = Field("offline", description="Translation engine (offline, ernie, google, deepl)")
-    preserve_structure: bool = Field(True, description="Preserve markdown structure")
-    engine_config: Optional[Dict[str, Any]] = Field(None, description="Engine-specific configuration")
-
-    class Config:
-        json_schema_extra = {
-            "example": {
-                "file_id": 1,
-                "source_lang": "zh",
-                "target_lang": "en",
-                "engine_type": "offline",
-                "preserve_structure": True,
-                "engine_config": {}
-            }
-        }
-
-
-class TranslationResponse(BaseModel):
-    """
-    Translation response schema (RESERVED)
-
-    Expected format for translation results
-    """
-    task_id: int = Field(..., description="Translation task ID")
-    file_id: int
-    source_lang: str
-    target_lang: str
-    engine_type: str
-    status: str = Field(..., description="Translation status (pending, processing, completed, failed)")
-    translated_file_path: Optional[str] = Field(None, description="Path to translated markdown file")
-    progress: float = Field(0.0, description="Translation progress (0.0-1.0)")
-    error_message: Optional[str] = None
-
-    class Config:
-        json_schema_extra = {
-            "example": {
-                "task_id": 1,
-                "file_id": 1,
-                "source_lang": "zh",
-                "target_lang": "en",
-                "engine_type": "offline",
-                "status": "processing",
-                "translated_file_path": None,
-                "progress": 0.5,
-                "error_message": None
-            }
-        }
-
-
-class TranslationStatusResponse(BaseModel):
-    """Translation task status response (RESERVED)"""
-    task_id: int
-    status: str
-    progress: float
-    created_at: str
-    completed_at: Optional[str] = None
-    error_message: Optional[str] = None
-
-
-class TranslationConfigRequest(BaseModel):
-    """Translation configuration request (RESERVED)"""
-    source_lang: str = Field(..., max_length=20)
-    target_lang: str = Field(..., max_length=20)
-    engine_type: str = Field(..., max_length=50)
-    engine_config: Optional[Dict[str, Any]] = None
-
-    class Config:
-        json_schema_extra = {
-            "example": {
-                "source_lang": "zh",
-                "target_lang": "en",
-                "engine_type": "offline",
-                "engine_config": {
-                    "model_path": "/path/to/model"
-                }
-            }
-        }
-
-
-class TranslationConfigResponse(BaseModel):
-    """Translation configuration response (RESERVED)"""
-    id: int
-    user_id: int
-    source_lang: str
-    target_lang: str
-    engine_type: str
-    engine_config: Optional[Dict[str, Any]] = None
-    created_at: str
-    updated_at: str
-
-
-class TranslationFeatureStatus(BaseModel):
-    """Translation feature status response"""
-    available: bool = Field(..., description="Whether translation is available")
-    status: str = Field(..., description="Feature status (reserved, planned, implemented)")
-    message: str = Field(..., description="Status message")
-    supported_engines: List[str] = Field(default_factory=list, description="Currently supported engines")
-    planned_engines: List[Dict[str, str]] = Field(default_factory=list, description="Planned engines")
-    roadmap: Dict[str, Any] = Field(default_factory=dict, description="Implementation roadmap")
-
-
-class LanguageInfo(BaseModel):
-    """Language information"""
-    code: str = Field(..., description="Language code (ISO 639-1)")
-    name: str = Field(..., description="Language name")
-    status: str = Field(..., description="Support status (planned, supported)")