Apply law-firm polish end-to-end #4791

Originally written by @ccantynz-alt on GitHub.
Imported from https://github.com/ccantynz-alt/voxlen/pull/10

Summary

Replaces the initial electric-blue "tech" palette with a restrained editorial treatment suited to professional/legal use, applied consistently across every surface the user encounters.

• Palette: deep oxford navy (marcoreid) + restrained brass accent; warm ink charcoal (dark) and warm parchment (light) surfaces.
• Typography: Fraunces variable serif for display/headings, Inter for body, JetBrains Mono for metadata. New label-caps small-caps utility.
• Elevation: soft multi-layer shadows replace neon glows; shadow-inset-hairline for depth. Dictation halo is now a warm brass shimmer.
• Surfaces touched: TitleBar, Sidebar, DictationPanel, TranscriptView, OnboardingWizard (all 4 steps), GrammarPanel, HistoryPanel, SettingsPanel (all tabs, shortcut recorder, voice-commands reference, privacy guarantee), AdminPanel.
• Primitives: Button (navy gradient + brass focus ring), Badge (small-caps uppercase, brass success), Input/Select (label-caps labels, brass focus), Switch (navy gradient track), Slider (navy-to-brass gradient track).

Test plan

• npx tsc --noEmit passes clean
• CI matrix build on main (macos aarch64/x86_64, windows, ubuntu-22.04) produces installers for v1.0.0 after merge

https://claude.ai/code/session_01MGWEMJqzYYhC8tCcjACCYM