固定生成规范参数并支持删除生成中占位

生成规范类图片固定提交 16:9、2K 和 gpt-image-2，并在面板底部只读展示。

生成中占位支持通过 Delete 或 Backspace 删除，不新增可见删除按钮。

异步生成回写前按生成对象 ID 校验，避免已删除占位重新落回画布。

更新编辑器生成面板与图片画布技术文档及相关测试。

src/index.css

@@ -5917,6 +5917,30 @@ button.image-canvas-editor__reference-chip:disabled {
   gap: 0.24rem;
 }
 
+.image-canvas-editor__readonly-generation-options {
+  display: inline-flex;
+  min-width: 0;
+  min-height: 2.25rem;
+  align-items: center;
+  gap: 0.28rem;
+  justify-self: start;
+  color: #475569;
+  font-size: 0.78rem;
+  font-weight: 820;
+}
+
+.image-canvas-editor__readonly-generation-options span {
+  display: inline-flex;
+  min-height: 1.72rem;
+  align-items: center;
+  justify-content: center;
+  border: 1px solid rgba(148, 163, 184, 0.18);
+  border-radius: 999px;
+  background: #f8fafc;
+  padding: 0 0.58rem;
+  white-space: nowrap;
+}
+
 .image-canvas-editor__context-menu {
   position: fixed;
   z-index: 35;
@@ -6325,6 +6349,7 @@ button.image-canvas-editor__reference-chip:disabled {
 
   .image-canvas-editor__option-cluster--dimensions,
   .image-canvas-editor__option-cluster--model,
+  .image-canvas-editor__readonly-generation-options,
   .image-canvas-editor__generation-submit,
   .image-canvas-editor__character-animation-submit {
     grid-column: auto;
@@ -6337,6 +6362,10 @@ button.image-canvas-editor__reference-chip:disabled {
     width: 100%;
   }
 
+  .image-canvas-editor__readonly-generation-options {
+    flex-wrap: wrap;
+  }
+
   .image-canvas-editor__character-composer {
     position: fixed;
     left: 0.75rem !important;