treewide(refactor): rename files to follow the same style

lib/controllers/key.dart

@@ -0,0 +1,30 @@
+import "package:flutter_riverpod/flutter_riverpod.dart";
+import "package:nexus/controllers/shared_prefs.dart";
+
+class KeyController extends Notifier<String?> {
+  final String key;
+  KeyController(this.key);
+
+  static const String spaceKey = "space";
+  static const String roomKey = "room";
+
+  @override
+  String? build() =>
+      ref.watch(SharedPrefsController.provider).requireValue.getString(key);
+
+  Future<void> set(String? value) async {
+    final prefs = ref.watch(SharedPrefsController.provider).requireValue;
+    state = value;
+
+    if (value == null) {
+      prefs.remove(key);
+    } else {
+      prefs.setString(key, value);
+    }
+  }
+
+  static final provider =
+      NotifierProvider.family<KeyController, String?, String>(
+        KeyController.new,
+      );
+}