refactor: unify OAuth providers with i18n support

- Introduce Provider interface pattern for standard OAuth protocols
- Create unified controller/oauth.go with common OAuth logic
- Add OAuthError type for translatable error messages
- Add i18n keys and translations (zh/en) for OAuth messages
- Use common.ApiErrorI18n/ApiSuccessI18n for consistent responses
- Preserve backward compatibility for existing routes and data

oauth/types.go

@@ -0,0 +1,59 @@
+package oauth
+
+// OAuthToken represents the token received from OAuth provider
+type OAuthToken struct {
+	AccessToken  string `json:"access_token"`
+	TokenType    string `json:"token_type"`
+	RefreshToken string `json:"refresh_token,omitempty"`
+	ExpiresIn    int    `json:"expires_in,omitempty"`
+	Scope        string `json:"scope,omitempty"`
+	IDToken      string `json:"id_token,omitempty"`
+}
+
+// OAuthUser represents the user info from OAuth provider
+type OAuthUser struct {
+	// ProviderUserID is the unique identifier from the OAuth provider
+	ProviderUserID string
+	// Username is the username from the OAuth provider (e.g., GitHub login)
+	Username string
+	// DisplayName is the display name from the OAuth provider
+	DisplayName string
+	// Email is the email from the OAuth provider
+	Email string
+	// Extra contains any additional provider-specific data
+	Extra map[string]any
+}
+
+// OAuthError represents a translatable OAuth error
+type OAuthError struct {
+	// MsgKey is the i18n message key
+	MsgKey string
+	// Params contains optional parameters for the message template
+	Params map[string]any
+	// RawError is the underlying error for logging purposes
+	RawError string
+}
+
+func (e *OAuthError) Error() string {
+	if e.RawError != "" {
+		return e.RawError
+	}
+	return e.MsgKey
+}
+
+// NewOAuthError creates a new OAuth error with the given message key
+func NewOAuthError(msgKey string, params map[string]any) *OAuthError {
+	return &OAuthError{
+		MsgKey: msgKey,
+		Params: params,
+	}
+}
+
+// NewOAuthErrorWithRaw creates a new OAuth error with raw error message for logging
+func NewOAuthErrorWithRaw(msgKey string, params map[string]any, rawError string) *OAuthError {
+	return &OAuthError{
+		MsgKey:   msgKey,
+		Params:   params,
+		RawError: rawError,
+	}
+}