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/IncomingCallPanel.tsx

@@ -0,0 +1,123 @@
+import type { ConversationSummary } from '@chat-app/shared/chat';
+import { useTranslation } from 'react-i18next';
+
+import { useCall } from '../context/CallContext';
+import { useFriendshipsContext } from '../context/FriendshipsContext';
+import { AvatarColorKey, colorKeyFor } from './CallParticipantTile';
+import { LockIcon, PhoneIcon, PhoneOffIcon } from './icons';
+
+interface Props {
+  conversation: ConversationSummary;
+}
+
+const PULSE_BG: Record<AvatarColorKey, string> = {
+  violet: 'bg-violet-200 text-violet-800 dark:bg-violet-900/60 dark:text-violet-200',
+  amber: 'bg-amber-200 text-amber-900 dark:bg-amber-900/60 dark:text-amber-200',
+  rose: 'bg-rose-200 text-rose-900 dark:bg-rose-900/60 dark:text-rose-200',
+  teal: 'bg-teal-200 text-teal-900 dark:bg-teal-900/60 dark:text-teal-200',
+};
+
+// Docked incoming-call panel: replaces the chat header, chat + composer stay
+// visible and usable below (per user decision). Full-bleed overlay lives in
+// the shell-level toast for cross-conversation ring notifications.
+export function IncomingCallPanel({ conversation }: Props) {
+  const { t } = useTranslation(['app']);
+  const { state, acceptIncoming, rejectIncoming } = useCall();
+  const { friendships } = useFriendshipsContext();
+
+  if (state.kind !== 'incoming' || state.conversationId !== conversation.id) return null;
+
+  const isGroup = conversation.type === 'group';
+  const callerProfile = conversation.members.find((m) => m.userId === state.fromUserId)?.profile ?? null;
+  const callerName =
+    callerProfile?.displayName ??
+    friendships.find((f) => f.peer.userId === state.fromUserId)?.peer.displayName ??
+    '?';
+  const groupName = isGroup ? (conversation.name ?? t('app:chats.new_group')) : null;
+  const title = isGroup ? groupName ?? callerName : callerName;
+  const letter = title.trim().charAt(0).toUpperCase() || '?';
+  const avatarUrl = isGroup
+    ? (conversation.avatarUrl ?? callerProfile?.avatarUrl ?? null)
+    : callerProfile?.avatarUrl ?? null;
+  const colorKey = colorKeyFor(state.fromUserId);
+  const avatarTone = PULSE_BG[colorKey];
+  const mediaLabel =
+    state.mediaKind === 'video' ? 'Video Call' : 'Voice Call';
+
+  return (
+    <section
+      role="region"
+      aria-label={t('app:call.incoming_title')}
+      className="relative overflow-hidden border-b border-line bg-surface-3"
+    >
+      <div className="absolute inset-0 bg-[radial-gradient(circle_at_30%_20%,rgba(79,70,229,0.10),transparent_60%),radial-gradient(circle_at_70%_80%,rgba(109,115,255,0.08),transparent_55%)]" />
+      <div className="relative mx-auto flex max-w-[480px] flex-col items-center px-6 py-8 text-center">
+        <p className="text-[12px] font-semibold uppercase tracking-[0.12em] text-fg-muted">
+          {t('app:call.incoming_title')}
+        </p>
+        <div className="relative my-4 flex h-[112px] w-[112px] items-center justify-center">
+          <span
+            aria-hidden="true"
+            className="pointer-events-none absolute inset-0 rounded-full border-2 border-accent animate-pulse-ring"
+          />
+          <span
+            aria-hidden="true"
+            className="pointer-events-none absolute inset-0 rounded-full border-2 border-accent animate-pulse-ring"
+            style={{ animationDelay: '1s' }}
+          />
+          {avatarUrl ? (
+            <img
+              src={avatarUrl}
+              alt={title}
+              className="h-24 w-24 rounded-full border-[3px] border-surface-3 object-cover"
+              draggable={false}
+            />
+          ) : (
+            <div
+              className={
+                'flex h-24 w-24 items-center justify-center rounded-full border-[3px] border-surface-3 font-display text-4xl font-bold ' +
+                avatarTone
+              }
+            >
+              {letter}
+            </div>
+          )}
+        </div>
+        <p className="font-display text-2xl font-bold tracking-tight text-fg">{title}</p>
+        <p className="mt-1.5 flex items-center gap-1.5 text-xs text-fg-muted">
+          <LockIcon className="h-3.5 w-3.5" />
+          <span>E2E verschlüsselt · {mediaLabel}</span>
+          {isGroup && (
+            <>
+              <span className="text-fg-muted/50" aria-hidden="true">·</span>
+              <span>
+                {t('app:call.incoming_group_from', {
+                  name: callerName,
+                  defaultValue: callerName + ' ruft an',
+                })}
+              </span>
+            </>
+          )}
+        </p>
+        <div className="mt-5 flex w-full max-w-[360px] gap-3">
+          <button
+            type="button"
+            onClick={rejectIncoming}
+            className="inline-flex flex-1 cursor-pointer items-center justify-center gap-2 rounded-[14px] border border-rose-500/40 bg-transparent px-5 py-3.5 text-sm font-semibold text-rose-600 transition hover:bg-rose-500/10 focus:outline-none focus-visible:ring-2 focus-visible:ring-rose-500/40 dark:text-rose-400"
+          >
+            <PhoneOffIcon className="h-4 w-4" />
+            <span>{t('app:call.decline')}</span>
+          </button>
+          <button
+            type="button"
+            onClick={() => void acceptIncoming()}
+            className="inline-flex flex-1 cursor-pointer items-center justify-center gap-2 rounded-[14px] bg-emerald-600 px-5 py-3.5 text-sm font-semibold text-white shadow-accept-btn transition hover:bg-emerald-500 focus:outline-none focus-visible:ring-2 focus-visible:ring-emerald-500/50"
+          >
+            <PhoneIcon className="h-4 w-4" />
+            <span>{t('app:call.accept')}</span>
+          </button>
+        </div>
+      </div>
+    </section>
+  );
+}