feat(call): Discord-style in-call features (group D)

- PiP widget now shows a live mm:ss / hh:mm:ss duration instead of the
  generic "tippe zum Öffnen" while a call is in progress.
- New ParticipantsPopover — portal-mounted, fixed bottom-right, lists
  everyone in the call with avatar, speaking ring, mute/deafen badges
  and a per-peer volume slider. Wired to CallControls via the users
  button (data-participants-trigger skips the outside-click dismiss
  while toggling).
- Non-terminal MicErrorBanner: getUserMedia failures inside joinRoom
  used to be silently swallowed by a console.error; they now set a
  categorized message (NotAllowedError / NotFoundError / NotReadableError)
  on CallContext.micError, render as a rose banner in both docked and
  fullscreen modes, and offer a Retry button that calls the extracted
  setupMicPipeline without rejoining the room.
- Screen-share toggle is now 1-click using the last-saved preset +
  displaySurface. Right-click on the share button still opens the
  quality dialog for users who want to adjust before starting.
- Noise-suppression toggle in the control bar (SparklesIcon). Flipping
  it updates audioSettings and hot-swaps the mic track via
  setAudioInputDevice so the new constraint takes effect without a
  rejoin. Mirrors Discord's Krisp button placement.
- Fullscreen auto-speaker now tracks "most recently started speaking"
  instead of "exactly one currently speaking", so two people briefly
  overlapping doesn't kick the focus back to grid. Tracked in a
  prevSpeakers ref against each activeSpeakers diff.
- Fullscreen controls auto-hide after 5s of mouse idle; mousemove /
  touchstart bring them back. Pinned visible while any popover
  (soundboard / volume-menu / participants / mic-error banner) is open
  so users can interact without the chrome fading mid-click.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop/src/components/CallUI.tsx

@@ -1,4 +1,4 @@
-import { useEffect } from 'react';
+import { useEffect, useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import { useLocation, useNavigate } from 'react-router-dom';
 
@@ -173,6 +173,13 @@ function PipCall() {
       : conv?.peer?.displayName ?? '—';
   const participantCount = 1 + remoteParticipants.length;
   const someoneSharing = remoteScreenShares.length > 0;
+  // Duration ticks while connected or reconnecting (LiveKit holds the room
+  // across reconnects, so the timer shouldn't reset on a wobble). Absent
+  // on outgoing/connecting where the call hasn't started yet.
+  const startedAt =
+    state.kind === 'connected' || state.kind === 'reconnecting'
+      ? state.startedAt
+      : null;
 
   return (
     <div
@@ -197,7 +204,11 @@ function PipCall() {
             aria-hidden="true"
             className="h-1.5 w-1.5 rounded-full bg-rose-500 animate-live-dot"
           />
-          <span>Live · {t('app:call.tap_to_open', { defaultValue: 'tippe zum Öffnen' })}</span>
+          <span className="tabular-nums">
+            {startedAt
+              ? <PipDuration startedAt={startedAt} />
+              : t('app:call.tap_to_open', { defaultValue: 'tippe zum Öffnen' })}
+          </span>
         </p>
       </div>
       <button
@@ -214,3 +225,24 @@ function PipCall() {
     </div>
   );
 }
+
+// Live-ticking `mm:ss` / `hh:mm:ss` for the PiP. Duplicated from InCallPanel
+// deliberately — the two widgets have different typography + tabular
+// contexts, and extracting a shared component would be heavier than the
+// 8-line countup it replaces.
+function PipDuration({ startedAt }: { startedAt: string }) {
+  const [, tick] = useState(0);
+  useEffect(() => {
+    const id = window.setInterval(() => tick((v) => v + 1), 1000);
+    return () => window.clearInterval(id);
+  }, []);
+  const total = Math.max(
+    0,
+    Math.floor((Date.now() - new Date(startedAt).getTime()) / 1000),
+  );
+  const hh = Math.floor(total / 3600);
+  const mm = Math.floor((total % 3600) / 60);
+  const ss = total % 60;
+  const pad = (n: number) => n.toString().padStart(2, '0');
+  return <>{hh > 0 ? `${hh}:${pad(mm)}:${pad(ss)}` : `${pad(mm)}:${pad(ss)}`}</>;
+}