fix(settings): skip the startup scan when dictionaries are already loaded

A second activity instance (PROCESS_TEXT) ran the full directory scan
again, and the main screen stayed blank until hasLoadedPreferences flipped
in the scan's finally block. The repository is a process-wide singleton:
when it already holds dictionaries, mark them up to date and load
preferences immediately.

app/src/main/java/com/example/research/ui/settings/SettingsViewModel.kt

@@ -277,7 +277,12 @@ class SettingsViewModel(
         var scanCompleted = false
         viewModelScope.launch {
             try {
-                scanCompleted = scanDirectoryInternal(preferencesManager.dictionaryPath) is OperationResult.Success
+                scanCompleted = if (localDictionaryRepository.dictionaries.value.isEmpty()) {
+                    scanDirectoryInternal(preferencesManager.dictionaryPath) is OperationResult.Success
+                } else {
+                    dictionaryStatus.value = DictionaryStatus.UpToDate
+                    false
+                }
             } catch (e: Exception) {
                 android.util.Log.e("SettingsViewModel", "Initial scan failed", e)
                 dictionaryStatus.value = if (localDictionaryRepository.dictionaries.value.isEmpty()) {