Responsive shell, theming system, and empty workspace create

[Modsofthenation]

Summary

UI pass for responsiveness, a real theming system, empty (non-demo) workspace create, and cleaner spacing/surfaces.

Responsive

• Mobile top bar + slide-out drawer nav (backdrop, Escape, body scroll lock)
• Grouped sidebar (Work / Review / Tools)
• Tighter phone breakpoints, safe-area padding, touch-sized controls

Theming

• Color mode: System / Dark / Light (follows OS when System)
• Accents: Teal / Ocean / Forest / Slate (data-accent + CSS tokens)
• Spacing / type tokens; Source Sans 3 + IBM Plex Mono
• Settings → Appearance controls; sidebar/topbar still toggle resolved light/dark

Empty workspace

• First-run choice: Empty workspace (seed: false) or Demo team
• Home / Team empty states when personCount === 0
• API path already supported; verified init → 0 people

Visual polish

• Consistent panel padding, panel titles, choice cards on unlock
• Brand/accent-aware borders (no hardcoded light-theme teal in dark CSS)

Screenshots

Settings appearance
Desktop grouped nav
Mobile drawer
Ocean accent

Test plan

• pnpm --filter @prm/ui build
• Empty init on temp PRM_DATA_DIR → personCount: 0
• Manual: Settings accents + mobile drawer
• Fresh data dir → Create empty workspace → Team empty state → add EM
• Fresh data dir → Demo team still seeds with workbench
• System color mode flips with OS preference

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