fix(mobile): show the session title beside the tabs on a landscape phone (#30879)

The served session page (react-native-web) reads flex: 0 as flex-basis 0%,
so the title block collapsed to zero width beside the tab strip. flex: -1
is natural width capped at 160, shrinking only when the row overflows, on
both web and native.

mobile/src/session/mobile-session-frame-styles.ts

@@ -57,8 +57,9 @@ export const mobileSessionFrameStyles = StyleSheet.create({
   },
   // Landscape phone: the tab strip takes the row's spare width instead of the title.
   sessionTitleBlockBesideTabs: {
-    flex: 0,
-    flexShrink: 1,
+    // -1, not 0: web reads flex 0 as a zero basis and collapses the title; -1 is natural width,
+    // shrinking only when the row overflows, on both web and native.
+    flex: -1,
     maxWidth: 160
   },
   sessionTitle: {