harden: debug mode logs only a request's origin and JSON-RPC method (closes #410)

With debug mode on, debugFetch logged every request's full URL and body,
so an RPC endpoint with an API key in its path or query string printed
that key to the console on every request. It now logs the HTTP method,
the URL's origin and, for a JSON-RPC body, the method name. The balance
refresh and token lookup log the RPC endpoint by its origin too. Failed
RPC calls print ethers' short message, since its full message for an
HTTP error carries the request URL. A failed endpoint check in settings
prints the endpoint's origin, since fetch's error for a URL with a user
name and password carries the whole URL. The README's DEBUG Mode Policy
says what debug mode logs.

Model: opus-5-5

src/popup/views/txStatus.js

@@ -133,7 +133,7 @@ function startWait(txInfo, txHash, broadcastTime, pollNow) {
             // failed — which matters most on a resumed wait, where the
             // first poll is already past the deadline.
             answered = false;
-            log.errorf("poll receipt failed:", e.message);
+            log.errorf("poll receipt failed:", e.shortMessage || e.message);
         }
         // The lookup is async: the wait may have ended while it was in
         // flight, in which case this result must not touch the view.