Let users choose the app appearance (Light / Dark / System)

[kud]

Handy already ships a full light palette and a full dark palette — but it always follows the OS, with no way to override it.

I'd like to add a simple Appearance setting: System (default, current behaviour), Light, or Dark.

Why I think this is worth it

To me this isn't really a "customization" request — it's the OS-standard behaviour that most apps already expose (Slack, VS Code, Discord, Notion, etc. all have it). My own case: my macOS is set to light, but I keep a lot of apps in dark because I prefer them that way, and I'd like Handy to be one of them.

How it's different from the accent-colour PRs (#1232, #551)

I know colour customization has been declined as brand identity. This is deliberately not that: it adds no new colours and changes nothing about the brand. It only lets you pick which of the two palettes @cjpais already designed is active — the same choice macOS itself offers under "Appearance". System remains the default.

Rough scope

• A theme setting (System/Light/Dark), defaulting to System.
• CSS data-theme overrides that beat the existing prefers-color-scheme media query.
• One dropdown in settings. The recording overlay keeps its own styling.

I have a working implementation ready to open as a PR. Happy to hear thoughts before it's considered. 🙏

[cjpais]

Would definitely accept this as as PR