feat: redesign + avatars + theme + call presence fixes (v0.6.0)

Visual:
- Light/dark theme via ThemeContext + CSS vars
- New design tokens (surface/fg/accent/line/etc.) across all pages
- Reusable Avatar component (img + letter fallback) wired into UserBar,
  ConversationHeader, ChatsPage, FriendsPage, GroupInfoPanel, IncomingCallPanel

Calls:
- Split call UI: IncomingCallPanel, InCallPanel, CallControls,
  CallParticipantTile, ScreenShareViewer
- Active speaker hook (useActiveSpeakers)
- Fix: ActiveCallBanner stayed hidden after hangup while peers in room.
  - useCallPresence: bind presence callbacks only when we own subscribe
    (Supabase forbids .on() after .subscribe() on shared dedup'd channels)
  - useCallPresence: never removeChannel — channel is shared with CallContext
    so tearing it down on ConversationHeader unmount killed live tracking
  - ActiveCallBanner: lastCallConversationId fallback so banner shows
    instantly after hangup, auto-dismiss when room confirmed empty
- Drop unused useAnyActiveCall

Bump tauri version 0.5.0 -> 0.6.0

apps/desktop/src/components/GroupInfoPanel.tsx

@@ -123,15 +123,25 @@ export function GroupInfoPanel({ open, onClose, conversation }: Props) {
             {conversation.members.map((m) => {
               const name = m.profile?.displayName ?? '?';
               const handle = m.profile?.username ? '@' + m.profile.username : '';
+              const avatarUrl = m.profile?.avatarUrl ?? null;
               const letter = name.trim().charAt(0).toUpperCase() || '?';
               return (
                 <li
                   key={m.userId}
                   className="flex items-center gap-3 rounded-lg px-2 py-1.5"
                 >
-                  <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-brand-500/30 text-xs font-semibold text-white ring-1 ring-brand-400/30">
-                    {letter}
-                  </div>
+                  {avatarUrl ? (
+                    <img
+                      src={avatarUrl}
+                      alt=""
+                      className="h-8 w-8 shrink-0 rounded-full object-cover"
+                      draggable={false}
+                    />
+                  ) : (
+                    <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-brand-500/30 text-xs font-semibold text-white ring-1 ring-brand-400/30">
+                      {letter}
+                    </div>
+                  )}
                   <div className="min-w-0 flex-1">
                     <p className="truncate text-sm text-white">
                       {name}
@@ -187,9 +197,18 @@ export function GroupInfoPanel({ open, onClose, conversation }: Props) {
                           onClick={() => void handleAdd(f.userId)}
                           className="flex w-full cursor-pointer items-center gap-3 rounded-lg px-2 py-1.5 text-left transition hover:bg-white/5 focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-400/40 disabled:opacity-60"
                         >
-                          <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-brand-500/30 text-xs font-semibold text-white ring-1 ring-brand-400/30">
-                            {letter}
-                          </div>
+                          {f.avatarUrl ? (
+                            <img
+                              src={f.avatarUrl}
+                              alt=""
+                              className="h-8 w-8 shrink-0 rounded-full object-cover"
+                              draggable={false}
+                            />
+                          ) : (
+                            <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-brand-500/30 text-xs font-semibold text-white ring-1 ring-brand-400/30">
+                              {letter}
+                            </div>
+                          )}
                           <div className="min-w-0 flex-1">
                             <p className="truncate text-sm text-white">{f.displayName}</p>
                             <p className="truncate text-xs text-neutral-500">@{f.username}</p>