feat: update SDK and GUI versions, add debugger protection settings

- Updated SDK_DECODER_SEMVER to "1.3.0" and GUI_SEMVER to "1.2.4" in config.ini.
- Updated MailViewer component to handle PDF already open error and improved iframe handling.
- Removed deprecated useMsgConverter setting from settings page.
- Added IsDebuggerRunning function to check for attached debuggers and quit the app if detected.
- Enhanced PDF viewer to prevent infinite loading and improved error handling.

Co-Authored-By: Laky-64 <iraci.matteo@gmail.com>

backend/utils/debug_windows.go

@@ -0,0 +1,11 @@
+package utils
+
+import "syscall"
+
+// IsDebugged reports whether a debugger is attached (Windows).
+func IsDebugged() bool {
+	kernel32 := syscall.NewLazyDLL("kernel32.dll")
+	isDebuggerPresent := kernel32.NewProc("IsDebuggerPresent")
+	ret, _, _ := isDebuggerPresent.Call()
+	return ret != 0
+}