refactor(userpage): move APIs into g0v0 private API

app/models/userpage.py

@@ -54,3 +54,47 @@ class ValidateBBCodeResponse(BaseModel):
     valid: bool = Field(description="BBCode是否有效")
     errors: list[str] = Field(default_factory=list, description="错误列表")
     preview: dict[str, str] = Field(description="预览内容")
+
+
+class UserpageError(Exception):
+    """用户页面处理错误基类"""
+
+    def __init__(self, message: str, code: str = "userpage_error"):
+        self.message = message
+        self.code = code
+        super().__init__(message)
+
+
+class ContentTooLongError(UserpageError):
+    """内容过长错误"""
+
+    def __init__(self, current_length: int, max_length: int):
+        message = f"Content too long. Maximum {max_length} characters allowed, got {current_length}."
+        super().__init__(message, "content_too_long")
+        self.current_length = current_length
+        self.max_length = max_length
+
+
+class ContentEmptyError(UserpageError):
+    """内容为空错误"""
+
+    def __init__(self):
+        super().__init__("Content cannot be empty.", "content_empty")
+
+
+class BBCodeValidationError(UserpageError):
+    """BBCode验证错误"""
+
+    def __init__(self, errors: list[str]):
+        message = f"BBCode validation failed: {'; '.join(errors)}"
+        super().__init__(message, "bbcode_validation_error")
+        self.errors = errors
+
+
+class ForbiddenTagError(UserpageError):
+    """禁止标签错误"""
+
+    def __init__(self, tag: str):
+        message = f"Forbidden tag '{tag}' is not allowed."
+        super().__init__(message, "forbidden_tag")
+        self.tag = tag