fix: Settings stores the URL on screen when another page stored a different one (closes #688)

The RPC and Blockscout "Save" buttons in Settings now set the URL in the stored record, inside the save. The save writes only the fields that differ from what the page last saved. So a "Save" of the URL that this page loaded kept another page's different URL stored. The flash message still read "Saved.". A save refused because the network changed still stores nothing.

Model: opus-5-5

tests/settingsEndpointSave.test.js

@@ -28,7 +28,7 @@ test.each([
         const page = await bootPopup(unversionedValidProfile());
         await page.click("btn-settings");
         const url = page.value(input);
-        // This write sends this page no storage change event.
+        // The browser is not made to tell this page of the other page's write.
         page.storage.write("autistmask", {
             ...page.storage.read("autistmask"),
             [field]: "https://other-page.example.invalid",