refactor(backend): 重构后端异常处理和模型管理

- 新增自定义异常类 BizException、NoteError 和 ProviderError
- 优化了模型管理相关的逻辑，包括加载、删除和测试连接等功能
- 改进了 Douyin 下载器的错误处理
- 调整了任务重试逻辑和笔记生成的异常处理- 更新了相关组件和页面以适应新的异常处理机制

backend/app/core/exception_handlers.py

@@ -1,38 +0,0 @@
-# app/core/exception_handlers.py
-from fastapi import Request, HTTPException
-from fastapi.exceptions import RequestValidationError
-from fastapi.responses import JSONResponse
-
-from app.utils.logger import get_logger
-from app.utils.response import ResponseWrapper
-from app.utils.status_code import StatusCode
-logger = get_logger(__name__)
-
-def register_exception_handlers(app):
-    @app.exception_handler(RequestValidationError)
-    async def validation_exception_handler(request: Request, exc: RequestValidationError):
-        errors = []
-        for err in exc.errors():
-            loc = err.get("loc", [])
-            field = loc[-1] if loc else "body"
-            msg = err.get("msg", "参数不合法")
-            errors.append({"field": field, "error": msg})
-        return JSONResponse(
-            status_code=400,
-            content=ResponseWrapper.error(msg="参数验证失败", code=StatusCode.PARAM_ERROR, data=errors)
-        )
-
-    @app.exception_handler(HTTPException)
-    async def http_exception_handler(request: Request, exc: HTTPException):
-        return JSONResponse(
-            status_code=exc.status_code,
-            content=ResponseWrapper.error(msg=str(exc.detail), code=StatusCode.FAIL)
-        )
-
-    @app.exception_handler(Exception)
-    async def global_exception_handler(request: Request, exc: Exception):
-        logger.exception(f"服务器内部错误: {exc}")
-        return JSONResponse(
-            status_code=500,
-            content=ResponseWrapper.error(msg="服务器内部错误", code=StatusCode.FAIL, data=str(exc))
-        )