feat(desktop): add persistent UI scaling

[katulevskiy]

Upstream mirror

Source: zeronsh#705
Original author: @katulevskiy
Original revision: fedfdd8e5737925db442bacfeb24ac5d9ae60850

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Add persistent whole-interface scaling in Settings → Appearance → Interface scale. The minus/plus controls and Ctrl+Shift+Plus / Ctrl+Shift+Minus adjust the UI from 50% to 200% in 10-point steps; Ctrl+Shift+0 resets to 100%. macOS also accepts Command equivalents.

Text, icons, spacing, and panes scale together without changing font preferences or native window dimensions. The device-local preference saves immediately and restores on startup. Pointer hit testing, pixel scrolling, IME coordinates, and native browser placement follow the selected scale. Reserved zoom shortcuts survive keymap edits and work from settings and a focused conversation composer.

Supporting dependency

Depends on zeronsh/zui#14, which adds independent GPUI window scaling. A temporary pinned Cargo patch makes this branch build and keeps GPUI and gpui-base on the same types. After that change merges, replace the patch with the upstream revision before merging this PR.

Validation

• All 1,433 Zeron UI tests passed (cargo test --locked -p zeron-ui --lib -- --test-threads=1).
• Both supporting GPUI scale regression tests passed.
• Desktop cargo check --locked -p zeron passed.
• Native Linux fixture checks shortcuts, immediate persistence, retained zoom after native bounds updates, and reset; captures use an isolated profile without engine/model calls.
• macOS/Windows live platform verification remains outstanding.

Screenshots

The same 1440 × 1080 native app window at each scale. Captured from the production shell using the reproducible fixture documented in docs/ui-scale.md.

Dark · 100%	Dark · 150%

Light · 120%:

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[contribution-manager-katulevskiy]

Contribution Manager

needs triage · medium risk · untriaged

Open review workspace · Revision aafc256f

Next actions:

• Direction decision needed
• Scope, risk, and platform triage needed
• Independent code review needed
• Required check: core-tests (missing)

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