User should be able to enable/disable dark mode in settings

[holmesworcester]

Right now we have a working dark mode, but it depends on detecting the OS dark/light mode setting and on some platforms (some Linux distros specifically) this does not work.

We'd like users to be able to set it in the app. See designs: https://www.figma.com/design/VT7uPXCIfmI9tbyhiAMhhu/Change-theme-(dark%2C-light%2C-system-modes)?node-id=637-470&t=WzGBAFFoIhIF72sm-0

This should override the detected OS settings if "dark" or "light" is selected. The default should be for it to depend on the OS setting.

ACCEPTANCE CRITERIA:

• a "theme" item in settings has three settings
• if set to "light" then Quiet will use the light theme
• if set to "dark" Quiet will use the dark theme
• if set to "system" Quiet will use the system theme, if detected.

[holmesworcester]

It's kind of janky for the user to set it per community but I think that's fine?

Autodetect can be an option. It might be greyed out on Windows.

[jgaylor]

@holmesworcester here's the Figma for draft 1.

1. Includes mobile: You mentioned we only need this for desktop, but I added mobile for good measure, and because the other apps I looked at deem it worthy.
2. Theme: calling this section "Theme" seems right to me if we don't provide any other customization at this time. I can see this being grouped under other categories like "Appearance" or "Advanced" when we have other things. For now it's less clicks to get here. "Appearance" also works as that's what I usually look for when trying to find this setting. WDYT?
3. Icons: A tangent, but I think we should probably add icons to the Community settings. It's growing, and harder to skim now. I think this would provide a nice visual cue for scanning, but needs to be applied to all.

[holmesworcester]

Looks great!

[jgaylor]

No thoughts on item 3?

[holmesworcester]

On item 3 I think we can wait until we've implemented enough of these options for it to require more scan-ability.

[jgaylor]

@holmesworcester This passed Design Finishing. Here's the latest Figma: Change theme (dark, light, auto)

[holmesworcester]

In case it's helpful, this is the original PR that added dark mode: #2521

(One of those commits should include the detection code, which this setting would interact with.)