feat: Discord Dark theme overhaul — darker palette, floating controls, UI polish

Shift entire color palette from Discord's Ash theme to the darker Dark theme.
Redesign VoiceControlBar as floating auto-show pill, add gradient Join Voice
screen, move invite icon to server header, add voice channel user status
badges, update auth pages with subtle gradient backgrounds, and sweep all
hardcoded hex colors across 14 files to match the new darker palette.

packages/web/src/components/voice/VoiceUser.tsx

@@ -91,7 +91,7 @@ export function VoiceUser({ participant, large }: VoiceUserProps) {
 
   return (
     <div
-      className={`relative bg-[#1e1f22] rounded-xl overflow-hidden flex items-center justify-center group transition-all duration-200 ${
+      className={`relative bg-[#111214] rounded-xl overflow-hidden flex items-center justify-center group transition-all duration-200 ${
         participant.isSpeaking
           ? 'ring-[3px] ring-discord-green shadow-[0_0_12px_rgba(35,165,90,0.25)]'
           : 'ring-1 ring-white/[0.06] hover:ring-white/10'
@@ -111,7 +111,7 @@ export function VoiceUser({ participant, large }: VoiceUserProps) {
           className={`w-full h-full ${large || isScreenShare ? 'object-contain bg-black' : 'object-cover'}`}
         />
       ) : (
-        <div className="w-full h-full flex flex-col items-center justify-center gap-3 bg-[#2b2d31]">
+        <div className="w-full h-full flex flex-col items-center justify-center gap-3 bg-[#1e1f22]">
           <div className="relative">
             <Avatar
               src={null}