Add resizable and collapsible panel layout

[tofarr]

Resurrected the resizer component. (This was in place last August)

Fixes #5894

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:505e8e0-nikolaik   --name openhands-app-505e8e0   docker.all-hands.dev/all-hands-ai/openhands:505e8e0

[neubig]

Thanks for this, a few notes!

1. I accidentally did some duplicate work and opened this PR, sorry: Fix issue #5894: Make it possible to collapse the right-hand side of the openhands screen #5896
2. Overall the code looks nice and it worked in my environment. But It seems to have introduced a regression with respect to the design being reactive to small screen widths. Here's the current one in this PR:

and main for reference:

[tofarr]

@neubig Responsive design should now work again:

[neubig]

This looks great code-wise, and I confirmed that all the functionality works as expected. Thanks for this, it'll be excellent to have!

[rbren]

Not sure what happened here but you can see it in the last screenshot there--there's a style regression here. Going to revert for now

[rbren]