fix(call): tile sizing polish + cinema-mode chrome suppression + spec/plan docs

Equal-grid cells no longer set aspect-video — on wide chat panels this
forced cell height = width × 9/16 (~400px on a 700px panel) which pushed
the row past the section's max-h and ate the controls bar below. n>=2
cells now fill grid tracks normally via auto-rows-fr; the solo case
(n=1) keeps a 16:9 silhouette via aspect-video + max-w + justify-self-
center so a single-user-alone-calling view doesn't stretch into a
full-width slab. Same change applied to the fullscreen-grid path plus
+16px bottom-padding (pb-28) so audio-only avatars' name chip clears
the floating controls bar.

Docked stage strip thumbs (focus + bento) switch from aspect-video
shrink-0 to flex-1 min-w-[200px] max-w-[460px] so 2-3 thumbs share the
row width evenly under the share above, instead of clinging to the left
edge with dead space to the right. Fullscreen-cinema strip keeps the
small aspect-video thumbs the user explicitly approved.

ScreenShareViewer gains a hideFullscreenToggle prop; cinema mode passes
it via a new `cinema` prop on TileRender so the in-share fullscreen icon
doesn't visually collide with FullscreenCall's strip-hidden toggle at
the same top-right corner.

docs/superpowers/specs + plans for the Discord-style tile handling
workstream are committed alongside the implementation that completed it.

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

apps/desktop/src/components/ScreenShareViewer.tsx

@@ -9,6 +9,11 @@ interface ScreenShareViewerProps {
   share: RemoteScreenShare;
   avatarUrl: string | null;
   displayName: string;
+  /** Suppress the in-share fullscreen toggle button. Used inside cinema
+   *  mode where (a) the window is already OS-fullscreen and (b) the
+   *  toggle collides visually with FullscreenCall's strip-hidden button
+   *  at the same top-right corner. */
+  hideFullscreenToggle?: boolean;
 }
 
 // Click-to-watch gate, live <video> attach/detach, native fullscreen toggle.
@@ -21,6 +26,7 @@ export function ScreenShareViewer({
   share,
   avatarUrl,
   displayName,
+  hideFullscreenToggle = false,
 }: ScreenShareViewerProps) {
   const { t } = useTranslation(['app']);
   const videoRef = useRef<HTMLVideoElement | null>(null);
@@ -76,7 +82,7 @@ export function ScreenShareViewer({
             defaultValue: displayName + ' teilt den Bildschirm',
           })}
         </span>
-        {watching && (
+        {watching && !hideFullscreenToggle && (
           <button
             type="button"
             onClick={toggleFullscreen}