feat(image): pass reference images to GPT image model for edits

Server: forward canvas/reference images to the image model so extract,
continue, and edit requests stay faithful to the source product.
- Add ImageRequestOptions.Images and route requests with inputs to the
  /v1/images/edits endpoint, via multipart upload (default) or JSON
  image_url payload, selectable through Agent.Image.InputImageTransport.
- Extract reference URLs from prompt directives, inline @image tokens,
  and chat message image/mask contents; fold them into the idempotency
  key and prepend a reference-fidelity instruction to the prompt.

Frontend:
- Shrink CanvasToast to a compact top pill.
- Paste an internal transparent clipboard node instead of re-uploading
  when it matches the clipboard image.
- Keep agent-project polling alive on stream error while streaming.

frontend/src/ui/components/CanvasToast/index.css

@@ -1,27 +1,30 @@
 .canvas-toast {
   position: fixed;
   left: 50%;
-  top: 48px;
+  top: 14px;
   z-index: 120;
-  width: min(1040px, calc(100vw - 140px));
-  min-height: 126px;
+  box-sizing: border-box;
+  width: fit-content;
+  min-width: 220px;
+  max-width: min(480px, calc(100vw - 32px));
+  min-height: 54px;
   display: flex;
   align-items: center;
-  gap: 28px;
-  padding: 0 44px;
+  gap: 12px;
+  padding: 12px 18px;
   border: 1px solid rgba(224, 229, 238, 0.96);
-  border-radius: 24px;
+  border-radius: 14px;
   color: #1f2329;
   background: rgba(255, 255, 255, 0.98);
-  box-shadow: 0 38px 90px rgba(17, 24, 39, 0.16);
+  box-shadow: 0 14px 36px rgba(17, 24, 39, 0.12);
   pointer-events: none;
   transform: translateX(-50%);
   animation: canvas-toast-enter 180ms cubic-bezier(0.2, 0, 0.2, 1);
 }
 
 .canvas-toast-icon {
-  width: 44px;
-  height: 44px;
+  width: 30px;
+  height: 30px;
   display: grid;
   place-items: center;
   flex: 0 0 auto;
@@ -29,6 +32,11 @@
   color: #ffffff;
 }
 
+.canvas-toast-icon svg {
+  width: 18px;
+  height: 18px;
+}
+
 .canvas-toast.success .canvas-toast-icon {
   background: #45d27c;
 }
@@ -40,9 +48,9 @@
 .canvas-toast strong {
   min-width: 0;
   overflow: hidden;
-  font-size: 32px;
-  font-weight: 850;
-  line-height: 1.18;
+  font-size: 15px;
+  font-weight: 750;
+  line-height: 1.32;
   text-overflow: ellipsis;
   white-space: normal;
   word-break: break-word;
@@ -62,26 +70,28 @@
 
 @media (max-width: 760px) {
   .canvas-toast {
-    top: 18px;
-    width: calc(100vw - 32px);
-    min-height: 76px;
-    gap: 14px;
-    padding: 16px 18px;
-    border-radius: 18px;
+    top: 0;
+    width: fit-content;
+    min-width: 0;
+    max-width: calc(100vw - 28px);
+    min-height: 50px;
+    gap: 10px;
+    padding: 11px 14px;
+    border-radius: 13px;
   }
 
   .canvas-toast-icon {
-    width: 32px;
-    height: 32px;
+    width: 28px;
+    height: 28px;
   }
 
   .canvas-toast-icon svg {
-    width: 20px;
-    height: 20px;
+    width: 17px;
+    height: 17px;
   }
 
   .canvas-toast strong {
-    font-size: 18px;
+    font-size: 14px;
     line-height: 1.28;
   }
 }