fix: perfect speaking ring circle and use real avatars/display names in voice tiles

Add flex to speaking ring wrapper divs in VoiceUser and PictureInPicture
to eliminate baseline descender space that made the ring oval. Extract
useVoiceParticipantMeta hook to resolve real display names and avatars
for voice participants instead of showing raw usernames with null avatars.

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

@@ -347,7 +347,7 @@ export function PictureInPicture() {
       ) : (
         <div className="w-full h-full flex items-center justify-center bg-surface-channel">
           {displayParticipant ? (
-            <div className="relative">
+            <div className="relative flex">
               <Avatar
                 name={displayParticipant.username}
                 size={64}