Add a mobile announcement banner about Polkadot SDK

[rzadp]

• Addresses this.

Here, we added an announcement banner about Polkadot SDK to the website. However it only shows up on desktop resolutions.

This introduces the same information as a form of a top announcement banner, visible on mobile resolutions.

• [x] This needs this PR to be merged first.

https://github.com/user-attachments/assets/0a532e7c-3afd-4587-be80-466010047a2a

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[rzadp]

For some reason the feature does not show on the Netlify deply preview, I don't know why. Could be something with caching dependencies?

It shows up locally.

[mordamax]

For some reason the feature does not show on the Netlify deply preview, I don't know why. Could be something with caching dependencies?

It shows up locally.

did you try to build locally with production mode?

i can see it in sources though, but not in the content of the pages layout

[rzadp]

did you try to build locally with production mode?

I did, same result.

It looks like it doesn't use updated version of git submodule gatsby-plugin-substrate

[rzadp]

It worked now after this: https://github.com/paritytech/substrate-website/pull/350/commits/516d26cd5486409e6a1a8d4dccca8a67ccca5065

It was also mentioned here.

[rzadp]

After triggering the cache invalidation, it appears now.

@mordamax Can you review it now?

Not sure it makes sense to dig deeper into this cache problem, since the website is being decommissioned.