feat: add theme preference (system/dark/light)

[baptisteArno]

CleanShot.2026-01-19.at.10.58.45.mp4

• Add theme preference to settings persistence and UI
• Resolve system theme and apply explicit theme class for consistent styling
• Align diff viewer syntax theme with the selected app theme

Decisions:

• Resolve system theme in JS (matchMedia) so CSS only needs one light palette block, avoiding duplicate @media + theme overrides.
• Add an app-level backdrop token to prevent OS appearance from bleeding through when forcing a theme.

[Dimillian]

Hmm completely removed transparency for me when I checked out this PR

[baptisteArno]

Ok let me investigate

[baptisteArno]

Do you confirm you have Reduce transparency off? And if you change that setting, you still can't see any transparency?

[Dimillian]

Yes I have it off and checking out your PR basically keep it off, but set the window background to be much darker almost like it's on?
On your PR

On Main

[baptisteArno]

Thanks for this, indeed I could reproduce and fix it 🙏

[Dimillian]

@codex review

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Apply light-theme variables outside the .app tree

The light theme variables are now scoped to .app.theme-light, which means any UI rendered outside the .app subtree will keep the dark defaults from :root. This shows up in portals like the workspace add menu (Sidebar.tsx uses createPortal(..., document.body)), which are no longer descendants of .app. When a user selects the light theme (or system is light), these popovers still render with dark colors, creating a mixed theme. Consider applying the theme class to body/:root or moving the light overrides there so portals inherit the correct variables.

Useful? React with 👍 / 👎.

[Dimillian]

CC @baptisteArno

[baptisteArno]

Requires deeper changes to make it work with native Window Vibrancy. Will open a new one.