Update ui-components & utilise new ff-theme-dark on signup/login (backport #2425)

[github-actions]

Backport of #2425

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Description

• In fixing Accept T&C checkbox on signup page broken #2419 noticed a more fundamental problem that had been bugging me for a while with ui-components in how it deals with dark theming (detailed here).
• These issues were meaning we had to write our own dark-them logic in /flowforge in some cases (due to slightly different bg colouring), which is nonsensical
• 0.7.0 of ui-components fixes that, and introduces a new ff-theme-dark class which will inherit the correct component-by-component CSS, and consequently fixes Accept T&C checkbox on signup page broken #2419

Examples:

<img width="499" alt="Screenshot 2023-07-06 at 15 21 16" src="https://github.com/flowforge/flowforge/assets/99246719/d84c1e8a-3aea-485c-ac2c-9e43433fd190\">

Related Issue(s)

Fixes #2419

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• CSS only changes

Labels

• Backport needed? -> add the backport label