Update Community and Thread Creation UI om Mobile Screensizes

This ticket updates the thread creation and community interaction UI with the following tasks:

Remove Bottom Create Button (Mobile Only):
- Remove the “Create” button displayed at the bottom of the screen when viewed on mobile screen sizes.
Mava Removal:
- Remove Mava functionality on mobile.
Floating Create Button:
- Add a floating “Create” button, available everywhere on the platform.
Thread Creation Page Updates:
- Allow users to always create threads from the thread creation page, regardless of their current location.
- If the user is outside a community, enable them to select a community to post into.

Design Devlink

Design Screenshot

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Additional Context

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@dillchen

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As a user on mobile, I should not see a “Create” button at the bottom of the screen.
As a mobile user, I should not see the Mava feature.
As a user, I should see a floating “Create” button accessible across the platform.
As a user, I should always be able to create a thread from the thread creation page, even if I am not in a community.
As a user, if I am not in a community, I should be able to select a community to post into when creating a thread.

Scroll right for the rest of the flow

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hicommonwealth / commonwealth