refactor(canvas): 重构画布助手面板组件结构

- 移除 Segmented 组件并替换为自定义模式切换按钮
- 替换 ModelPicker 为 ComposerModelPill 组件
- 添加下拉菜单实现模型选择功能
- 优化 CSS 样式类和响应式布局
- 更新图标引入和工具栏组件结构
- 简化提示词库按钮样式配置

web/src/app/(user)/canvas/components/canvas-prompt-library.tsx

@@ -16,9 +16,9 @@ export function CanvasPromptLibrary({ onSelect }: { onSelect: (prompt: string) =
         <>
             <Tooltip title="提示词库">
                 <Button
-                    shape="circle"
-                    className="!h-8 !w-8 !min-w-8 shrink-0 !bg-transparent"
-                    style={{ borderColor: theme.node.stroke, color: theme.node.text }}
+                    type="text"
+                    className="!h-8 !w-8 !min-w-8 shrink-0 !rounded-full !bg-transparent !p-0"
+                    style={{ color: theme.node.text }}
                     icon={<BookOpen className="size-3.5" />}
                     onClick={() => setOpen(true)}
                     aria-label="提示词库"