feat: file variety, user status, DND gate, drag-drop, mentions, link preview, emoji picker, soundboard, ringtone

Attachments
- Video: native <video controls>, decrypted blob, metadata preload
- PDF: collapsible <object> viewer with download + preview toggle
- Generic: file card with lazy decrypt, mime-to-extension map
- MessageBubble dispatch: audio/image/video/pdf/generic by mime
- Composer accept widened from image/* to any; AttachmentPreview renders
  non-images as file cards

User status
- usePeerPresence returns { state, statusMessage } and tracks both fields
  via realtime updates
- ConversationHeader subtitle shows custom status_message when peer is
  online/idle/dnd (with message set); falls back to localized presence
  label; always "Offline" when state === 'offline'
- UserBar: status_message input in dropdown (max 128 chars, save on
  blur/Enter), subtitle uses same precedence as peer view
- AuthContext: auto-flip offline → online on session mount; best-effort
  offline on beforeunload/pagehide; respects explicit idle/dnd/invisible
- i18n: presence.status_placeholder (DE + EN)

DND
- CallUI: incoming ring suppressed when own presence === 'dnd' (outgoing
  rings stay audible — user-initiated)
- CallContext: presenceRef mirrors profile.presenceState, incoming-call
  and missed-call OS notifications skipped under DND
- ConversationsContext already gated message tone + notify

Drag/drop + paste
- Page-root drag handlers feed ingestFiles; overlay shown while dragging
- Textarea onPaste extracts clipboard image items

@mentions in groups
- MentionAutocomplete: keyboard-driven dropdown, arrow/enter/tab/esc
- Composer onChange parses trailing @token, auto-open
- renderBodyWithMentions highlights @username tokens in bubbles

Link previews
- Migration 20260421000003_link_previews.sql (cache table, auth read,
  service-role write via edge function)
- Edge function og-preview: POST {url}, fetches HTML (6s timeout, 1MB
  cap), regex-parses OG/twitter/description, upserts cache
- useLinkPreview hook with in-memory cache + inflight dedup
- LinkPreviewCard rendered from first URL in message body

Emoji picker
- Built-in curated set (~250 emojis) across five categories
- Search by keyword/emoji char/category, recent list persisted in
  localStorage
- Trigger button next to + and voice buttons in composer

Soundboard + ringtone + mic pipeline
- Pulled in (user-authored) SoundboardManagerDialog/Panel/Settings,
  RingtoneSettings, mic pipeline + hotkeys + storage modules
- AuthContext imports updateOwnProfile for presence auto-flip

Fixes
- AttachmentAudio min-width so bubbles don't collapse to 0px on peer
  side
- Focus flicker: visibility/online wake refresh throttled to 30s,
  focus listener dropped, loading flag only on first fetch

apps/desktop/src/components/MentionAutocomplete.tsx

@@ -0,0 +1,103 @@
+import type { ConversationSummary } from '@chat-app/shared/chat';
+import { useEffect, useState } from 'react';
+
+import { Avatar } from './Avatar';
+
+interface Props {
+  members: ConversationSummary['members'];
+  query: string;
+  excludeUserId: string | undefined;
+  onSelect: (username: string) => void;
+  onClose: () => void;
+}
+
+// Dropdown shown above the composer when the user has typed `@` followed
+// by the start of a member name. Keyboard-first — arrow keys move through,
+// enter/tab commits, escape cancels.
+export function MentionAutocomplete({
+  members,
+  query,
+  excludeUserId,
+  onSelect,
+  onClose,
+}: Props) {
+  const q = query.toLowerCase();
+  const matches = members
+    .filter((m) => m.userId !== excludeUserId)
+    .filter((m) => {
+      if (!q) return true;
+      const name = (m.profile?.displayName ?? '').toLowerCase();
+      const handle = (m.profile?.username ?? '').toLowerCase();
+      return name.includes(q) || handle.includes(q);
+    })
+    .slice(0, 8);
+
+  const [active, setActive] = useState(0);
+  useEffect(() => {
+    setActive(0);
+  }, [query]);
+
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if (matches.length === 0) return;
+      if (e.key === 'ArrowDown') {
+        e.preventDefault();
+        setActive((i) => (i + 1) % matches.length);
+      } else if (e.key === 'ArrowUp') {
+        e.preventDefault();
+        setActive((i) => (i - 1 + matches.length) % matches.length);
+      } else if (e.key === 'Enter' || e.key === 'Tab') {
+        e.preventDefault();
+        const pick = matches[active];
+        if (pick?.profile?.username) onSelect(pick.profile.username);
+      } else if (e.key === 'Escape') {
+        e.preventDefault();
+        onClose();
+      }
+    };
+    window.addEventListener('keydown', onKey, true);
+    return () => {
+      window.removeEventListener('keydown', onKey, true);
+    };
+  }, [matches, active, onSelect, onClose]);
+
+  if (matches.length === 0) return null;
+
+  return (
+    <div
+      role="listbox"
+      aria-label="Mitglieder"
+      className="absolute bottom-full left-0 right-0 z-20 mb-2 max-h-64 overflow-y-auto rounded-xl border border-line bg-surface-2 p-1 shadow-xl"
+    >
+      {matches.map((m, idx) => {
+        const name = m.profile?.displayName ?? m.profile?.username ?? '?';
+        const handle = m.profile?.username ?? '';
+        const isActive = idx === active;
+        return (
+          <button
+            key={m.userId}
+            type="button"
+            role="option"
+            aria-selected={isActive}
+            onMouseEnter={() => setActive(idx)}
+            onClick={() => {
+              if (m.profile?.username) onSelect(m.profile.username);
+            }}
+            className={
+              'flex w-full cursor-pointer items-center gap-2 rounded-lg px-2 py-1.5 text-left text-sm transition ' +
+              (isActive ? 'bg-accent/20 text-fg' : 'text-fg-muted hover:bg-surface-3')
+            }
+          >
+            <Avatar
+              displayName={name}
+              url={m.profile?.avatarUrl ?? null}
+              className="h-6 w-6 text-[10px]"
+            />
+            <span className="min-w-0 flex-1 truncate text-fg">{name}</span>
+            <span className="shrink-0 text-[10px] text-fg-muted">@{handle}</span>
+          </button>
+        );
+      })}
+    </div>
+  );
+}