fix: use CSS zoom for UI scaling to avoid terminal selection offsets

[Dimillian]

Motivation

• The terminal selection and cursor coordinates drift when the app UI is scaled via transform: scale(...), so the UI scale should avoid transforming the coordinate system used by canvas-like components (e.g., xterm.js).

Description

• Replaced the transform-based scaling on the root .app with zoom: var(--ui-scale, 1) in src/styles/base.css while keeping the existing size compensation via height/width calculations.
• Added an @supports not (zoom: 1) fallback that restores the previous transform: scale(...) behavior for engines that do not support zoom so older/unsupported runtimes remain functional.
• Updated the .app.ui-scale-default case to use zoom: 1 (and transform: none in the fallback) so default scale removes any scaling.

Testing

• Ran npm run lint (ESLint) which completed successfully.
• Ran npm run typecheck (tsc --noEmit) which completed successfully.

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Codex Task

[Dimillian]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Swish!

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