feat: Generate VTuber character sheet with expression assets

The Gemini service has been updated to generate a character sheet rather than a single avatar image. This sheet includes the main character and separate assets for closed eyes and an open mouth.

The `AvatarConfig` type and `RiggingEditor` component have been extended to handle these new expression assets (`textureClosedEye`, `textureOpenMouth`). A new `Sprite` component has been added to `Studio.tsx` to correctly render these specific regions from the generated character sheet. The UI has been updated to reflect the new generation process.

services/geminiService.ts

@@ -1,25 +1,30 @@
+
 import { GoogleGenAI } from "@google/genai";
 
 /**
- * Generates a VTuber avatar image based on user description.
+ * Generates a VTuber avatar character sheet.
  * Uses gemini-3-pro-image-preview for high quality.
  */
 export const generateAvatarImage = async (description: string): Promise<string> => {
   try {
     // Initialize client inside the function to ensure we use the most up-to-date API key
-    // after the user has completed the selection flow.
     const ai = new GoogleGenAI({ apiKey: process.env.API_KEY });
 
-    // We construct a prompt that encourages a good format for a 2D avatar (front facing, clean background)
     const prompt = `
-      Create a high-quality, flat 2D anime or stylized character illustration suitable for a VTuber avatar.
-      The character should be facing forward (front view).
-      The background should be a solid, single color (white or bright green) to allow for easy removal or masking.
+      Create a VTuber character sheet with a flat 2D anime style.
+      
+      LAYOUT:
+      1. MAIN CHARACTER (Left side, takes up 70% of width):
+         - Front-facing view, head and shoulders.
+         - Neutral expression, eyes open, mouth closed.
+      
+      2. EXPRESSION ASSETS (Right side, vertical column):
+         - Top: The same character's face with EYES CLOSED (for blinking).
+         - Bottom: The same character's face with MOUTH OPEN (for talking).
       
       Character Description: ${description}
       
-      Style: Vibrant, clean lines, detailed eyes.
-      Focus: Head and shoulders only.
+      Style: Vibrant, clean lines, solid white or green background for easy keying.
     `;
 
     const response = await ai.models.generateContent({
@@ -31,7 +36,7 @@ export const generateAvatarImage = async (description: string): Promise<string>
       },
       config: {
         imageConfig: {
-          aspectRatio: "1:1",
+          aspectRatio: "16:9", // Wide to fit character sheet
           imageSize: "1K"
         }
       }