feat: voice messages, offline queue, delivery ticks, volume slider, admin + scaling

- Voice messages: MediaRecorder → encrypted attachment, custom waveform
  player via OfflineAudioContext, 60s limit + live mic-level meter
- Offline message queue: localStorage outbox, exponential backoff retries,
  optimistic pending bubble with retry/discard
- Delivery indicator: message_deliveries table + RLS (reciprocal receipts),
  ✓ / ✓✓ / ✓✓-blue tick states, group-aware (all members must ack)
- Per-participant volume slider in calls via right-click tile menu,
  persisted to localStorage, applied to attached audio elements
- Group call scaling: grid up to 12 tiles with pagination,
  active-speaker auto-promotion in fullscreen
- Push notifications scaffolding: service worker, VAPID subscription
  registration, notify-push edge function skeleton
- Backup recovery code: 24-char base32 code (~120 bits entropy) as
  alternative decrypt path, restore UI with mode toggle
- Admin panel: conversations list, audit log (admin_audit_log table +
  admin_log_action RPC), audit entry on user flag toggle
- Search v2: sender filter, attachment-only toggle, date range
- Reactions pop animation (scale 0.4→1.15→1 on count change)
- Message list windowing (150 default, expand via IntersectionObserver)
- Stub cleanup: removed dead ScreenshareStub from CallParticipantTile

Fixes:
- Focus-triggered flicker: dropped window.focus listeners in three spots,
  throttled visibilitychange/online wake-refreshes to 30s, keep existing
  data visible during background re-syncs (no more spinner on every click)
- Voice attachment audio element collapsed to 0px on peer side — now
  forces 280px min-width on bubble

Migrations (push required):
  20260421000001_message_deliveries.sql
  20260421000002_admin_audit_log.sql

Server TODO:
  VAPID keys + notify-push edge function deploy

apps/desktop/src/components/ParticipantVolumeMenu.tsx

@@ -0,0 +1,87 @@
+import { useEffect, useState } from 'react';
+import { createPortal } from 'react-dom';
+
+import {
+  getParticipantVolume,
+  setParticipantVolume,
+  subscribeParticipantVolumes,
+} from '../lib/participantVolumes';
+
+interface Props {
+  userId: string;
+  displayName: string;
+  x: number;
+  y: number;
+  onClose: () => void;
+}
+
+const MENU_W = 240;
+const MENU_H = 84;
+
+export function ParticipantVolumeMenu({
+  userId,
+  displayName,
+  x,
+  y,
+  onClose,
+}: Props) {
+  const [volume, setVolume] = useState<number>(() => getParticipantVolume(userId));
+
+  // Re-sync from store in case another menu instance changed the same user.
+  useEffect(() => subscribeParticipantVolumes(() => {
+    setVolume(getParticipantVolume(userId));
+  }), [userId]);
+
+  // Outside click + Esc to close.
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') onClose();
+    };
+    const onDown = (e: MouseEvent) => {
+      const target = e.target as HTMLElement | null;
+      if (target?.closest('[data-volume-menu]')) return;
+      onClose();
+    };
+    window.addEventListener('keydown', onKey);
+    window.addEventListener('mousedown', onDown);
+    return () => {
+      window.removeEventListener('keydown', onKey);
+      window.removeEventListener('mousedown', onDown);
+    };
+  }, [onClose]);
+
+  const left = Math.min(Math.max(8, x), window.innerWidth - MENU_W - 8);
+  const top = Math.min(Math.max(8, y), window.innerHeight - MENU_H - 8);
+
+  return createPortal(
+    <div
+      data-volume-menu
+      role="dialog"
+      aria-label={'Lautstärke ' + displayName}
+      style={{ left, top, width: MENU_W }}
+      className="fixed z-[80] rounded-xl border border-line bg-surface-2/95 p-3 shadow-xl backdrop-blur-md"
+    >
+      <div className="mb-2 flex items-center justify-between gap-2 text-xs">
+        <span className="truncate font-semibold text-fg">{displayName}</span>
+        <span className="tabular-nums text-fg-muted">
+          {Math.round(volume * 100)}%
+        </span>
+      </div>
+      <input
+        type="range"
+        min={0}
+        max={1}
+        step={0.01}
+        value={volume}
+        onChange={(e) => {
+          const v = Number(e.target.value);
+          setVolume(v);
+          setParticipantVolume(userId, v);
+        }}
+        aria-label={'Lautstärke ' + displayName}
+        className="w-full accent-accent"
+      />
+    </div>,
+    document.body,
+  );
+}