Add TNEF handling and email loading improvements

- Implement TNEF extraction and recursive parsing in new `tnef_reader.go` and associated tests.
- Create tests for TNEF extraction scenarios in `tnef_diag_test.go`, `tnef_diag7_test.go`, and `tnef_diag8_test.go`.

frontend/src/lib/wailsjs/go/main/App.js

@@ -2,10 +2,34 @@
 // Cynhyrchwyd y ffeil hon yn awtomatig. PEIDIWCH Â MODIWL
 // This file is automatically generated. DO NOT EDIT
 
+export function CheckForUpdates() {
+  return window['go']['main']['App']['CheckForUpdates']();
+}
+
 export function CheckIsDefaultEMLHandler() {
   return window['go']['main']['App']['CheckIsDefaultEMLHandler']();
 }
 
+export function ConvertToUTF8(arg1) {
+  return window['go']['main']['App']['ConvertToUTF8'](arg1);
+}
+
+export function CreateBugReportFolder() {
+  return window['go']['main']['App']['CreateBugReportFolder']();
+}
+
+export function DetectEmailFormat(arg1) {
+  return window['go']['main']['App']['DetectEmailFormat'](arg1);
+}
+
+export function DownloadUpdate() {
+  return window['go']['main']['App']['DownloadUpdate']();
+}
+
+export function ExportSettings(arg1) {
+  return window['go']['main']['App']['ExportSettings'](arg1);
+}
+
 export function FrontendLog(arg1, arg2) {
   return window['go']['main']['App']['FrontendLog'](arg1, arg2);
 }
@@ -14,6 +38,10 @@ export function GetConfig() {
   return window['go']['main']['App']['GetConfig']();
 }
 
+export function GetCurrentMailFilePath() {
+  return window['go']['main']['App']['GetCurrentMailFilePath']();
+}
+
 export function GetImageViewerData() {
   return window['go']['main']['App']['GetImageViewerData']();
 }
@@ -30,10 +58,30 @@ export function GetStartupFile() {
   return window['go']['main']['App']['GetStartupFile']();
 }
 
+export function GetUpdateStatus() {
+  return window['go']['main']['App']['GetUpdateStatus']();
+}
+
 export function GetViewerData() {
   return window['go']['main']['App']['GetViewerData']();
 }
 
+export function ImportSettings() {
+  return window['go']['main']['App']['ImportSettings']();
+}
+
+export function InstallUpdate(arg1) {
+  return window['go']['main']['App']['InstallUpdate'](arg1);
+}
+
+export function InstallUpdateSilent() {
+  return window['go']['main']['App']['InstallUpdateSilent']();
+}
+
+export function InstallUpdateSilentFromPath(arg1) {
+  return window['go']['main']['App']['InstallUpdateSilentFromPath'](arg1);
+}
+
 export function IsDebuggerRunning() {
   return window['go']['main']['App']['IsDebuggerRunning']();
 }
@@ -46,6 +94,10 @@ export function OpenEMLWindow(arg1, arg2) {
   return window['go']['main']['App']['OpenEMLWindow'](arg1, arg2);
 }
 
+export function OpenFolderInExplorer(arg1) {
+  return window['go']['main']['App']['OpenFolderInExplorer'](arg1);
+}
+
 export function OpenImage(arg1, arg2) {
   return window['go']['main']['App']['OpenImage'](arg1, arg2);
 }
@@ -62,10 +114,18 @@ export function OpenPDFWindow(arg1, arg2) {
   return window['go']['main']['App']['OpenPDFWindow'](arg1, arg2);
 }
 
+export function OpenURLInBrowser(arg1) {
+  return window['go']['main']['App']['OpenURLInBrowser'](arg1);
+}
+
 export function QuitApp() {
   return window['go']['main']['App']['QuitApp']();
 }
 
+export function ReadAuto(arg1) {
+  return window['go']['main']['App']['ReadAuto'](arg1);
+}
+
 export function ReadEML(arg1) {
   return window['go']['main']['App']['ReadEML'](arg1);
 }
@@ -86,6 +146,30 @@ export function SaveConfig(arg1) {
   return window['go']['main']['App']['SaveConfig'](arg1);
 }
 
+export function SaveScreenshot() {
+  return window['go']['main']['App']['SaveScreenshot']();
+}
+
+export function SaveScreenshotAs() {
+  return window['go']['main']['App']['SaveScreenshotAs']();
+}
+
+export function SetCurrentMailFilePath(arg1) {
+  return window['go']['main']['App']['SetCurrentMailFilePath'](arg1);
+}
+
+export function SetUpdateCheckerEnabled(arg1) {
+  return window['go']['main']['App']['SetUpdateCheckerEnabled'](arg1);
+}
+
 export function ShowOpenFileDialog() {
   return window['go']['main']['App']['ShowOpenFileDialog']();
 }
+
+export function SubmitBugReport(arg1) {
+  return window['go']['main']['App']['SubmitBugReport'](arg1);
+}
+
+export function TakeScreenshot() {
+  return window['go']['main']['App']['TakeScreenshot']();
+}