feat: add configurable composer shortcuts (model / access / reasoning)

[Dimillian]

Motivation

• Provide keyboard shortcuts to speed up composer workflows by cycling model, access mode, and reasoning mode, and let users customize them from Settings.

Description

• Add generic shortcut utilities in src/utils/shortcuts.ts including parseShortcut, formatShortcut, buildShortcutValue, and matchesShortcut to parse, format and match shortcut strings.
• Implement useComposerShortcuts hook in src/features/composer/hooks/useComposerShortcuts.ts to listen for shortcut keys (when the composer textarea is focused) and cycle the selected model, access mode, or reasoning option.
• Persist new settings fields (composerModelShortcut, composerAccessShortcut, composerReasoningShortcut) in types and defaults across frontend and backend (src/types.ts, src/features/settings/hooks/useAppSettings.ts, and src-tauri/src/types.rs).
• Add a Shortcuts section to the Settings UI with capture/clear controls and display using formatShortcut (src/features/settings/components/SettingsView.tsx) and a small CSS tweak for shortcut inputs (src/styles/settings.css).
• Wire the hook into the app lifecycle in src/App.tsx so composer shortcuts are active and cycle the correct UI state via existing setters (setSelectedModelId, setAccessMode, setSelectedEffort).

Testing

• Ran npm run lint (ESLint) and it completed successfully.
• Ran npm run typecheck (tsc --noEmit) and it completed successfully.
• Attempted npm run tauri build and it failed during the Rust build step due to a missing system dependency (glib-2.0 required by glib-sys), which is an environment issue unrelated to the TypeScript changes.

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Codex Task

[Dimillian]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Bravo.

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