Screen sharing: start dialog, sound, video tiles and a meeting view

- Start dialog with source list, live preview, sound and quality choices
- Sound on Linux through PipeWire: one program or everything except this
  app, fed into a virtual microphone and kept linked as programs come and go;
  system loopback on Windows; stereo Opus
- A sharer's tile shows the picture; clicking it opens a large view with the
  other tiles as a strip. Own stream is previewed in the own tile
- Stream volume for viewers, watch and stop from the profile panel
- Unit tests for the PipeWire link planner; the proxy test no longer writes to
  the root channel other tests listen in

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

electron/preload.ts

@@ -21,8 +21,12 @@ contextBridge.exposeInMainWorld('mumh5Native', {
   onContextMenu: (fn: (params: unknown) => void) => { ipcRenderer.on('context-menu', (_e, p) => fn(p)); },
   editAction: (action: string, arg?: unknown) => ipcRenderer.send('edit:action', action, arg),
   onTrayAction: (fn: (action: string) => void) => { ipcRenderer.on('tray:action', (_e, a: string) => fn(a)); },
-  screenSources: () => ipcRenderer.invoke('share:sources'),
+  screenSources: (thumbnails: boolean) => ipcRenderer.invoke('share:sources', !!thumbnails),
   pickScreenSource: (id: string) => ipcRenderer.send('share:pick', id),
+  shareInfo: () => ipcRenderer.invoke('share:info'),
+  shareAudioApps: () => ipcRenderer.invoke('share:audioApps'),
+  shareAudioStart: (target: unknown) => ipcRenderer.invoke('share:audioStart', target),
+  shareAudioStop: () => ipcRenderer.invoke('share:audioStop'),
   describeCerts: (ders: Uint8Array[]) => ipcRenderer.invoke('certs:describe', ders),
   identities: {
     list: () => ipcRenderer.invoke('identities:list'),