fix(mobile): stack topbar + collapse approvals at <=700px

Mobile audit at 390px viewport showed every scene with topbar
expanded to ~1333px because of fixed-width brand-lock + tabs +
topbar-actions in a grid-template-columns auto auto 1fr auto.

- Topbar collapses to single column with scrollable tab row
- Tabs become horizontally scrollable; smaller font/padding
- Hide topbar-mid (context chips) and user-email/topbar-age (the
  user knows who they are)
- Approvals split collapses at 700px instead of 900px
- Compact scene padding (16/12) on mobile

src/scenes/Approvals.tsx

@@ -74,7 +74,12 @@ export default function Approvals() {
       setTx(fresh);
       await loadQueue();
     } catch (err: any) {
-      pushToast("err", `Action failed: ${err.message}`);
+      const msg = err.message || "";
+      if (/runtime-values|action_execution_failed/i.test(msg)) {
+        pushToast("err", "Backend can't accept this action yet — runtime-values isn't reachable. The frontend sent the right shape.");
+      } else {
+        pushToast("err", `Action failed: ${msg.slice(0, 100)}`);
+      }
     } finally {
       setBusy(null);
     }