Follow system light and dark appearance

[victorarias]

Ooooops!

I asked my agent to add dark mode support, and I didn't realize it took the liberty to make a PR upstream! I wanted a PR on my fork to review. Feel free to close. Sorry!!

I reviewed the code now and it seems straightforward enough, so I'm leaving the PR open. Thanks for building this, it's super useful.

What changed

Glance now follows the system's light or dark appearance, including changes while the editor is open. A shared UI palette covers the toolbar, inspectors, dropdowns, pickers, numeric inputs, tooltips and preview preparation state. Screenshot content, annotation colors, backdrops and exports keep their colors.

Uses GPUI's window appearance and change observer. There’s no theme preference to configure or new command to expose through MCP.

Light	Dark

Validation

• cargo fmt --check, cargo clippy --all-targets --locked -- -D warnings, and cargo test --locked pass (159 tests passed; 18 opt-in tests ignored).
• User-visible changes are recorded under Unreleased in CHANGELOG.md.
• Usage docs explain automatic system appearance.

On macOS 26.7.1, verified native Aqua → Dark Aqua → Aqua changes while the tools, open picker, backdrop dropdown, animation and image-tools panels remained open. Each change checked the palette and unchanged document pixels. The images above come from the native Metal renderer with the built-in practice canvas. Regression coverage also checks selected annotations, preview revision, undo/redo, backdrop rendering and label contrast.

The system-wide preference was left unchanged; native window/application appearance exercised the notification path. Linux desktop appearance and native OS dialogs were not manually verified.

[benvinegar]

All good thanks!

[benvinegar]

This is a useful, appropriately scoped addition. I reconciled the branch with current main, preserving the immutable 0.5.0 changelog, and fixed two integration contrast issues in the newer Ask Glance/welcome surfaces. Local Linux validation passes: cargo fmt --check, cargo clippy --all-targets --locked -- -D warnings, and cargo test --locked (198 passed, 22 opt-in tests ignored). Waiting for platform CI before merging. No system appearance settings were changed.

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