feat: merge Voice, Media, and Recordings into unified Live panel

- New LivePanel component combines voice bridge, media player, screen share, and recordings
- Single page layout: voice controls → audio visualizer + active speakers → now playing → music/screen/recordings tabs
- Reduced tabs from 6 to 4: Live, Messages, Analytics, Review
- Sidebar updated with new tab structure
- Default tab changed from 'voice' to 'live'
- Cleaner compact layout with icon buttons and inline controls
- Recordings sub-panel with user avatars, status badges, and download buttons

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/layout/Sidebar.tsx

@@ -1,13 +1,11 @@
-import { Bot, BarChart3, MessageSquare, Music2, ShieldAlert, Volume2, Mic } from "lucide-react";
+import { Bot, BarChart3, MessageSquare, ShieldAlert, Radio } from "lucide-react";
 import type { DashboardTab } from "../../types/ui";
 import { cn } from "../../lib/utils";
 import { Button } from "../ui/button";
 
-const navItems: Array<{ id: DashboardTab; label: string; icon: typeof Volume2 }> = [
-  { id: "voice", label: "Voice", icon: Volume2 },
-  { id: "media", label: "Media", icon: Music2 },
+const navItems: Array<{ id: DashboardTab; label: string; icon: typeof Radio }> = [
+  { id: "live", label: "Live", icon: Radio },
   { id: "messages", label: "Messages", icon: MessageSquare },
-  { id: "recordings", label: "Recordings", icon: Mic },
   { id: "analytics", label: "Analytics", icon: BarChart3 },
   { id: "review", label: "Review", icon: ShieldAlert },
 ];