fix: a network switch in Settings updates the testnet banner at once (closes #511)

The Settings network handler now redraws the red banner once the switch
is saved, so it appears on a switch to Sepolia and goes on a switch back
to mainnet while Settings is still on screen. Before, the banner changed
only when the next screen came up. The Chrome browser suite switches
both ways on Settings and reads the banner each time.

Model: opus-5-5

src/popup/views/settings.js

@@ -343,11 +343,13 @@ function init(ctx) {
         // switch request.
         notify({ type: "AUTISTMASK_NETWORK_CHANGED", chainId: net.chainId });
         resetRenderedViews();
-        // Settings itself is brought up to date for the new network here.
+        // Settings itself, and the testnet banner above it, are brought up
+        // to date for the new network here.
         markViewRendered("settings");
         $("settings-rpc").value = state.rpcUrl;
         $("settings-blockscout").value = state.blockscoutUrl;
         renderTrackedTokens();
+        updateDebugBanner(state.currentView);
         showFlash("Switched to " + net.name + ".");
     });