feat: add internal skg infinite canvas

THIRD_PARTY_NOTICES.md

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+# Third Party Notices
+
+## huobao-canvas
+
+Portions of the internal SKG canvas module are adapted from `chatfire-AI/huobao-canvas`.
+
+- Source: https://github.com/chatfire-AI/huobao-canvas
+- License note: the upstream README declares MIT licensing and links to a `LICENSE` file, but the cloned snapshot used for this integration did not include that file.
+- Local integration path: `web/canvas-app/`
+- SKG changes: branding, visible product text, model options, auth behavior, and API calls were changed for SKG internal use.
+
+This notice is kept in the repository for engineering traceability and is not shown in the product UI.