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/ui/components/CanvasAgentComposer/index.css

@@ -433,15 +433,24 @@
   font-weight: 600;
 }
 
-.composer-quality-control {
+.composer-quality-control,
+.composer-resolution-control {
   display: grid;
-  grid-template-columns: repeat(4, minmax(0, 1fr));
   overflow: hidden;
   border-radius: 999px;
   background: #f4f4f4;
 }
 
-.composer-quality-control button {
+.composer-quality-control {
+  grid-template-columns: repeat(4, minmax(0, 1fr));
+}
+
+.composer-resolution-control {
+  grid-template-columns: repeat(3, minmax(0, 1fr));
+}
+
+.composer-quality-control button,
+.composer-resolution-control button {
   height: 40px;
   border-radius: 999px;
   color: #3a414d;
@@ -449,7 +458,8 @@
   font-size: 14px;
 }
 
-.composer-quality-control button.selected {
+.composer-quality-control button.selected,
+.composer-resolution-control button.selected {
   border: 1px solid #c9ced7;
   background: #fff;
 }