feat: Add user settings for voice and persona

Introduces a new `UserSettings` interface and default settings. This allows users to customize voice preferences (name, style, gender) and persona characteristics within the application. This enhances personalization and user experience by tailoring interactions to individual needs and preferences.

types.ts

@@ -10,12 +10,18 @@ export interface Scenario {
   cbtFocus: string[];
 }
 
+export interface UserSettings {
+  voiceName: 'Puck' | 'Charon' | 'Kore' | 'Fenrir' | 'Zephyr';
+  vocalStyle: string;
+  genderPreference: 'Male' | 'Female' | 'Neutral';
+}
+
 export interface Message {
   id: string;
   role: 'user' | 'model' | 'system';
   text: string;
   timestamp: Date;
-  isAnalysis?: boolean; // If true, this is a CBT analysis, not part of roleplay
+  isAnalysis?: boolean;
 }
 
 export type SessionMode = 'text' | 'voice';