fix: an open popup follows a network switch the background saves (closes #650)

When the background saves a network switch after the user approves a
site's request, an open popup now notices the stored record change and
takes the new network from it, holding the lock, inside a save. It then
leaves the page as a switch in Settings does: the stack is cut, every
screen counts as not yet rendered, and the screen on top is drawn again.
The cut and the redraw are now two functions in the Settings view that
both paths call. A record already on the popup's network, such as its
own Settings switch, changes nothing. The popup never switches the
network itself.

Model: opus-5-5

tests/trackedTokensPerNetwork.test.js

@@ -161,6 +161,7 @@ test("a token added by contract address on Sepolia is tracked on Sepolia only",
     );
     expect(stored().trackedTokens).toEqual([SEPOLIA_TOKEN]);
 
+    await boot.click("btn-settings");
     await chooseNetwork(boot, "mainnet");
     expect(stored().networkId).toBe("mainnet");
     expect(stored().trackedTokens).toEqual([MAINNET_TOKEN]);