Refactor App composition helpers

[Dimillian]

Motivation

• Reduce imperative logic in the composition root by extracting window-label detection and localStorage-backed transparency state into dedicated hooks to improve testability and separation of concerns.

Description

• Add useWindowLabel in src/features/layout/hooks/useWindowLabel.ts to encapsulate getCurrentWindow() label lookup and return a stable window label via a hook.
• Add useTransparencyPreference in src/features/layout/hooks/useTransparencyPreference.ts to encapsulate the reduceTransparency localStorage state and its persistence.
• Update src/App.tsx to import and use useWindowLabel and useTransparencyPreference, removing the inline getCurrentWindow logic and the manual localStorage effect.

Testing

• Ran npm run lint, which executed but reported a TypeScript compatibility warning from @typescript-eslint due to the local TypeScript version; no new lint errors introduced.
• Ran npm run typecheck, which completed successfully with no type errors.

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Codex Task

[Dimillian]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Chef's kiss.

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