feat: 接入形态图库与 Seedream 生图操作

展示已有主图、候选图和失败记录，支持单图及批量生成、主图选择。
补充正式 ID 校验、费用确认、图片加载占位和回归测试。
依赖后端 eac8dc3 的项目形态图库只读接口。

src/styles.css

@@ -614,6 +614,72 @@
         background: #8a9b6f;
         box-shadow: 0 0 0 3px #e9edde;
     }
+    .dialog-content.dialog-wide {
+        width: min(820px, calc(100vw - 36px));
+    }
+    .form-image-grid {
+        display: grid;
+        grid-template-columns: repeat(auto-fill, minmax(min(260px, 100%), 1fr));
+        gap: 20px;
+    }
+    .form-image-card {
+        overflow: hidden;
+    }
+    .asset-image {
+        display: grid;
+        place-items: center;
+        width: 100%;
+        aspect-ratio: 4 / 3;
+        overflow: hidden;
+        background: #eff0e9;
+    }
+    .asset-image img {
+        width: 100%;
+        height: 100%;
+        object-fit: contain;
+        min-height: 0;
+    }
+    .asset-image-empty {
+        display: flex;
+        align-items: center;
+        justify-content: center;
+        flex-direction: column;
+        gap: 10px;
+        padding: 20px;
+        color: var(--color-muted);
+        font-size: 11px;
+        text-align: center;
+    }
+    .asset-image-preview {
+        aspect-ratio: auto;
+        height: min(48vh, 480px);
+    }
+    .image-history {
+        display: flex;
+        gap: 12px;
+        overflow-x: auto;
+        padding: 4px;
+    }
+    .image-history-item {
+        width: 110px;
+        flex-shrink: 0;
+        padding: 4px;
+        border: 1px solid var(--color-line);
+        border-radius: 4px;
+    }
+    .image-history-item.selected {
+        border-color: var(--color-accent);
+        background: #faf2ed;
+    }
+    .image-history-item .asset-image-empty {
+        font-size: 9px;
+        padding: 6px;
+        gap: 4px;
+    }
+    .image-history-item .asset-image-empty svg {
+        width: 14px;
+        height: 14px;
+    }
     .storyboard-controls {
         display: grid;
         grid-template-columns: minmax(180px, 1fr) 100px 145px auto;