Add frontend themes

[reaper47]

The web app currently supports two themes:

• Light
• Dark

The theme currently follows the system's current theme.

DaisyUI has a bunch of nice themes already available to us: https://daisyui.com/docs/themes/

The goal of this issue is to:

• Add those themes to the CSS
• Verify how much larger the CSS file becomes after adding them. If too large, select the best-looking ones.
• Let the user select one of those themes from the settings
• The user may select "Follow system"

[mblennegard]

Maybe this is already one of the differences between different themes, but regardless of selected it would be nice if a user can define their own sizes for different text sections, e.g. making the text in the Instructions or Ingredients sections larger.

[reaper47]

Accessibility features are definitely important. Here's the related issue: #395.