fix: PersonalDictionaryView preview and AppGroupStore dictionary writes

Use ThemedRoot in preview instead of inaccessible ThemePalette().
Add setPersonalDictionary(_:) for let AppGroupStore bindings; use
it from PersonalDictionaryView and DictionaryLearner.

Co-authored-by: Rocky <hkgood@users.noreply.github.com>

OSGKeyboard/Services/DictionaryLearner.swift

@@ -144,7 +144,7 @@ final class DictionaryLearner {
 
         if didChange {
             dictionary.version += 1
-            store.personalDictionary = dictionary
+            store.setPersonalDictionary(dictionary)
         }
         // Suppress the "did not change" path; we still return the
         // bumped-counts view so the caller can refresh a UI label.

OSGKeyboard/Views/PersonalDictionaryView.swift

@@ -224,11 +224,14 @@ struct PersonalDictionaryView: View {
 
     private func persist() {
         dictionary.version += 1
-        store.personalDictionary = dictionary
+        store.setPersonalDictionary(dictionary)
     }
 }
 
+#if DEBUG
 #Preview {
-    PersonalDictionaryView()
-        .environment(\.themePalette, ThemePalette())
+    ThemedRoot {
+        PersonalDictionaryView()
+    }
 }
+#endif