feat(image): integrate PoloX image editing workflows

Add WaveSpeed image editing and image tools plugins, canvas image editing workflows, layer selection, and Cloud Agent image tools with approval-safe transient references.

plugin-packages/image-tools/README.md

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+# Image Tools
+
+影策图片工具协议插件，提供去背景和图层拆分两个异步能力。
+
+## 能力
+
+- `image-tools-remove-background`：`bria/remove-background`
+- `image-tools-layer-decomposition`：`bytedance/seedream-v5.0-pro/layer-decomposition`
+
+两个 provider 都接受统一的 `images[]` 源图输入，结果 URL 会由宿主下载并持久化。