fix(admin): enable image generation permission for Composite groups

- Add 'composite' to imagePricingPlatforms set in groupsImagePricing.ts
- Allow Composite groups to toggle allow_image_generation in admin UI
- Backend already supports allow_image_generation field for all platforms
- Add test case to verify Composite platform is included

Fixes #5369

frontend/src/views/admin/__tests__/groupsImagePricing.spec.ts

@@ -27,6 +27,11 @@ describe("groups image pricing platform support", () => {
     expect(supportsImagePricingPlatform("anthropic")).toBe(false);
   });
 
+  it("includes Composite groups in image pricing controls", () => {
+    expect(supportsImagePricingPlatform("composite")).toBe(true);
+    expect(imagePricingPlatforms.has("composite")).toBe(true);
+  });
+
   it("keeps image and video pricing copy separate", () => {
     expect(imagePricingI18nKey("grok", "title")).toBe(
       "admin.groups.imagePricing.title",

frontend/src/views/admin/groupsImagePricing.ts

@@ -1,5 +1,6 @@
 export const imagePricingPlatforms = new Set([
   "antigravity",
+  "composite",
   "gemini",
   "grok",
   "openai",