feat: Add Gmail API sync workflow and integrate related data models

src/modules/error/code.rs

@@ -48,6 +48,8 @@ pub enum ErrorCode {
     SmtpConnectionFailed = 50040,
     MailBoxNotCached = 50050,
     AutoconfigFetchFailed = 50060,
+    GmailApiCallFailed = 50070,
+    GmailApiInvalidHistoryId = 50080,
 
     // Message queue errors (60000–60999)
     NatsRequestFailed = 60000,
@@ -83,6 +85,8 @@ impl ErrorCode {
             ErrorCode::InternalError
             | ErrorCode::AutoconfigFetchFailed
             | ErrorCode::ImapCommandFailed
+            | ErrorCode::GmailApiCallFailed
+            | ErrorCode::GmailApiInvalidHistoryId
             | ErrorCode::ImapUnexpectedResult
             | ErrorCode::HttpResponseError
             | ErrorCode::NatsRequestFailed