feat: audio devices + fullscreen + banner cleanup (v0.7.0)

Audio device selection:
- audioSettings: persisted inputDeviceId + outputDeviceId
- CallContext: uses stored input deviceId on mic enable, new
  setAudioInputDevice / setAudioOutputDevice actions that hot-swap
  without reconnect. Output swap applies HTMLMediaElement.setSinkId
  to every attached remote-audio element (LiveKit's switchActiveDevice
  only tracks elements it attached itself)
- SettingsPage: new "Mikrofon" + "Ausgabegerät" selects with
  enumerateDevices, devicechange listener, permission-probe button.
  setSinkId-unsupported fallback is messaged but non-blocking

Fullscreen:
- FullscreenCall was absolute inset-0 z-40 which trapped it inside the
  <main> pane — sidebar + chat-list stayed visible. Switched to
  fixed inset-0 z-[60] so the call overlays the whole window
  Discord-style
- ScreenShareViewer fullscreen: CSS-only toggle (native Fullscreen API
  unreliable under Tauri WKWebView), portalled to document.body when
  active so no ancestor stacking context can clip it. Esc exits

ActiveCallBanner:
- cleanup effect returned early when presence was entirely empty,
  leaving the "1 im Raum" fallback stuck after both peers left. Now
  schedules dismissLastCall as soon as othersIn.length === 0, with a
  3s grace window to absorb presence re-sync flicker

Bump tauri version 0.6.0 -> 0.7.0

apps/desktop/src/components/ConversationHeader.tsx

@@ -210,17 +210,14 @@ function ActiveCallBanner({ conversationId }: { conversationId: string }) {
   const justLeft = state.kind === 'idle' && lastCallConversationId === conversationId;
 
   // Once presence confirms the room is empty, drop the "just left" hint so the
-  // banner hides cleanly instead of sticking forever.
+  // banner hides cleanly instead of sticking forever. Grace window handles the
+  // brief gap between hangup and presence re-sync so we don't flicker.
   useEffect(() => {
     if (!justLeft) return;
-    if (active.length === 0) return;
-    if (othersIn.length === 0) {
-      // Active reports only us (or something stale) — wait, then dismiss.
-      const id = window.setTimeout(() => dismissLastCall(), 3000);
-      return () => window.clearTimeout(id);
-    }
-    return undefined;
-  }, [justLeft, active.length, othersIn.length, dismissLastCall]);
+    if (othersIn.length > 0) return; // still live — keep banner
+    const id = window.setTimeout(() => dismissLastCall(), 3000);
+    return () => window.clearTimeout(id);
+  }, [justLeft, othersIn.length, dismissLastCall]);
 
   if (iAmIn) return null;
   if (othersIn.length === 0 && !justLeft) return null;

apps/desktop/src/components/InCallPanel.tsx

@@ -487,7 +487,7 @@ function FullscreenCall({
   }, []);
 
   return (
-    <div className="absolute inset-0 z-40 flex flex-col overflow-hidden bg-surface">
+    <div className="fixed inset-0 z-[60] flex flex-col overflow-hidden bg-surface">
       <div className="relative min-h-0 flex-1">
         {speaker && (
           <div className="absolute inset-0">

apps/desktop/src/components/ScreenShareViewer.tsx

@@ -1,5 +1,6 @@
 import type { RemoteTrack } from 'livekit-client';
 import { useEffect, useRef, useState } from 'react';
+import { createPortal } from 'react-dom';
 import { useTranslation } from 'react-i18next';
 
 import type { RemoteScreenShare } from '../context/CallContext';
@@ -32,30 +33,31 @@ export function ScreenShareViewer({ share, avatarUrl, displayName }: ScreenShare
     };
   }, [share.track, watching]);
 
+  // Esc exits CSS fullscreen.
   useEffect(() => {
-    const onChange = () => {
-      setIsFullscreen(document.fullscreenElement === containerRef.current);
+    if (!isFullscreen) return;
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') setIsFullscreen(false);
     };
-    document.addEventListener('fullscreenchange', onChange);
-    return () => document.removeEventListener('fullscreenchange', onChange);
-  }, []);
+    window.addEventListener('keydown', onKey);
+    return () => window.removeEventListener('keydown', onKey);
+  }, [isFullscreen]);
 
+  // CSS-only "app fullscreen" — Discord-style: overlay the whole window
+  // including the left sidebar + chat list. Native Fullscreen API is
+  // unreliable in Tauri's WKWebView and doesn't add useful chrome-hiding
+  // beyond what `fixed inset-0 z-[60]` already gives us.
   const toggleFullscreen = () => {
-    const el = containerRef.current;
-    if (!el) return;
-    if (document.fullscreenElement === el) {
-      void document.exitFullscreen();
-    } else {
-      void el.requestFullscreen();
-    }
+    setIsFullscreen((v) => !v);
   };
 
-  return (
+  const viewerNode = (
     <div
       ref={containerRef}
       className={
-        'overflow-hidden rounded-xl border border-emerald-500/30 bg-black ' +
-        (isFullscreen ? 'flex h-screen w-screen flex-col rounded-none' : '')
+        isFullscreen
+          ? 'fixed inset-0 z-[60] flex h-screen w-screen flex-col overflow-hidden border-0 bg-black'
+          : 'overflow-hidden rounded-xl border border-emerald-500/30 bg-black'
       }
     >
       <div className="flex shrink-0 items-center gap-2 border-b border-emerald-500/20 bg-emerald-500/15 px-3 py-1.5 text-xs text-emerald-700 dark:text-emerald-200">
@@ -130,6 +132,14 @@ export function ScreenShareViewer({ share, avatarUrl, displayName }: ScreenShare
       )}
     </div>
   );
+
+  // When in fullscreen, portal out of the call-panel subtree into <body> so
+  // no ancestor can clip or stack below us. Sidebar/chat-list are siblings of
+  // AppShell's root — portalled node sits above them via z-[60].
+  if (isFullscreen) {
+    return createPortal(viewerNode, document.body);
+  }
+  return viewerNode;
 }
 
 function BlurredTile({ avatarUrl, letter }: { avatarUrl: string | null; letter: string }) {