feat(canvas): resolution/ratio composer settings and quality/count controls

Replace the ratio-baked size presets with a resolution tier (1K/2K/4K) plus
ratio selection and normalized dimensions, send imageQuality/imageCount to
the agent, and add the output_format field to GeneratorTaskInputArgs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/domain/design.ts

@@ -137,6 +137,7 @@ export type GeneratorTaskInputArgs = {
   aspect_ratio?: string;
   image?: string[];
   image_url?: string;
+  output_format?: string;
   prompt?: string;
   resolution?: string;
   src_box?: NormalizedBox;
@@ -327,6 +328,8 @@ export type AgentChatPayload = {
   mode?: string;
   imageModel?: string;
   imageSize?: string;
+  imageQuality?: string;
+  imageCount?: number;
   enableWebSearch?: boolean;
   messages: Array<{
     role: "user";