fix: the Settings network help text says switching restores the last endpoints used (closes #513)

The text under Network said switching resets the RPC and Blockscout
endpoints to their defaults. Switching actually restores the endpoints
last used on that network, or that network's defaults if it has none,
as README's Settings section says. The text now says that, in README's
words.

Model: opus-5-5

src/popup/index.html

@@ -924,9 +924,9 @@
                 <div class="bg-well p-3 mx-1 mb-3">
                     <h3 class="font-bold mb-1">Network</h3>
                     <p class="text-xs text-muted mb-1">
-                        Select the Ethereum network. Switching networks will
-                        update the RPC and Blockscout endpoints to their
-                        defaults.
+                        Select the Ethereum network. Switching restores the RPC
+                        and Blockscout endpoints last used on that network, or
+                        that network's defaults if it has none.
                     </p>
                     <div class="text-xs flex items-center gap-1">
                         <select