feat(frontend): IMPHNEN design deep integration — full 5-layer redesign

Layer 0 — Foundation:
- Dark mode palette (30+ CSS var pairs in [data-theme='dark'])
- CSS-first theme engine in styles.css (@theme + CSS vars)
- UseTheme hook with light/dark/system support + localStorage persistence
- Fixed animation keyframes (shimmer 1.5s canonical, glowPulse moved to CSS)
- Smooth theme switch transitions via .theme-transitioning class

Layer 1 — Shared UI Components:
- Badge: success/warning variants now use CSS vars (bg-success-soft text-success)
- Toast: rewritten with CSS vars, z-index fixed (40), repositioned top-right
- Skeleton: added variant prop (rounded/circular/rectangular)
- EmptyState: new component with icon + title + description + action
- Button: added tertiary variant + icon-sm size
- Card: added elevated/bordered variants
- Input: added soft variant

Layer 2 — Layout & Navigation:
- TabStrip: new horizontal tab navigation with spring underline indicator (z-30)
- Sidebar: expanded by default (w-64), brand assets always visible
- Header: simplified brand bar, removed redundant page titles, added ThemeToggle
- MobileTabBar: enhanced with spring dot indicator + glass bg + safe area
- DashboardLayout: integrated TabStrip between Header and content
- ParticleBackground: lazy render, skips on mobile/reduced-motion

Layer 3 — Feature Components:
- MessageCard: 30+ hardcoded hex replacements → semantic CSS vars
- MessagesPanel: stat badges use Badge component variants
- DashboardStats: StatCard with variant system (primary/success/warning/destructive)
- UserSummaryList/UserProfileDetail/ChannelProfileDetail: all hardcoded colors → CSS vars
- AudioVisualizer: reads --primary CSS var at paint time
- ActiveSpeakers/RecordingsSubPanel: hardcoded colors → CSS vars

Layer 4 — Polish:
- EmptyState integrated across messages/dashboard/live panels
- Theme toggle wired in Header + App root
- Hover state audit for consistency
- Entry animations verified (cardStagger/cardItem pattern in all panels)

Resolves DESIGN_TOKENS.md §13.x issues: hardcoded colors, shimmer mismatch,
glow-pulse fragmentation, z-index collisions, toast positioning.

services/frontend/src/features/live/components/AudioVisualizer.tsx

@@ -40,9 +40,12 @@ export function AudioVisualizer({ levels }: AudioVisualizerProps) {
     const barWidth = width / levels.length;
     const maxBarHeight = height * 0.85;
 
+    const root = getComputedStyle(document.documentElement);
+    const primaryColor = root.getPropertyValue("--primary").trim() || "#23a1eb";
+
     const gradient = ctx.createLinearGradient(0, 0, 0, height);
-    gradient.addColorStop(0, "#23a1eb");
-    gradient.addColorStop(1, "#3eb0f2");
+    gradient.addColorStop(0, primaryColor);
+    gradient.addColorStop(1, primaryColor);
 
     for (let i = 0; i < levels.length; i++) {
       const level = levels[i];