add molab share action (#9207)

## 📝 Summary

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Adds molab share action which opens up `molab.marimo.io/new#code/...` in
a new tab. This is shown if either sharing option is enabled, but not
shown if both are disabled.

<img width="400" height="205" alt="image"
src="https://github.com/user-attachments/assets/0c8a80af-585d-41a3-8d09-1a2796df4b81"
/>


https://github.com/user-attachments/assets/c10a116b-3c5b-46cc-ade8-bd93aade8a3e

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- [ ] For large changes, or changes that affect the public API: this
change was discussed or approved through an issue, on
[Discord](https://marimo.io/discord?ref=pr), or the community
[discussions](https://github.com/marimo-team/marimo/discussions) (Please
provide a link if applicable).
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## ✅ Merge Checklist

- [x] I have read the [contributor
guidelines](https://github.com/marimo-team/marimo/blob/main/CONTRIBUTING.md).
- [ ] Documentation has been updated where applicable, including
docstrings for API changes.
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Author: Light2Dark

frontend/src/components/editor/actions/useNotebookActions.tsx

@@ -381,6 +381,18 @@ export function useNotebookActions() {
             });
           },
         },
+        {
+          icon: <MarimoPlusIcon size={14} strokeWidth={1.5} />,
+          label: "Create molab notebook",
+          handle: async () => {
+            const code = await readCode();
+            const url = createShareableLink({
+              code: code.contents,
+              baseUrl: `${Constants.molab}/new`,
+            });
+            window.open(url, "_blank");
+          },
+        },
       ],
     },
 

frontend/src/core/constants.ts

@@ -7,6 +7,7 @@ export const Constants = {
   discordLink: "https://marimo.io/discord?ref=notebook",
   docsPage: "https://docs.marimo.io",
   youtube: "https://www.youtube.com/@marimo-team",
+  molab: "https://molab.marimo.io",
 };
 
 export const KnownQueryParams = {