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

TODO.md

@@ -45,6 +45,19 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-04: Debug mode no longer writes RPC API keys to the console
+  ([#410](https://git.eeqj.de/sneak/AutistMask/issues/410)). `debugFetch` logged
+  every request's full URL and body, so an RPC endpoint with a key in its path
+  or query string printed that key on every request. It now logs the HTTP
+  method, the URL's origin and, for a JSON-RPC call, the method name. The
+  balance refresh and token lookup log the RPC endpoint by its origin too. A
+  failed RPC call's error line prints the error's short message, which names the
+  HTTP status, not its full message, which carries the request URL. A failed
+  endpoint check in settings names the endpoint by its origin, not the `fetch`
+  error's message, which carries the whole URL, password included, for a URL
+  with a user name and password. The README's DEBUG Mode Policy says what debug
+  mode logs.
+
 - 2026-10-04: A site has at most one connection prompt and one signature prompt
   open at a time ([#405](https://git.eeqj.de/sneak/AutistMask/issues/405)). Each
   `eth_requestAccounts` or `personal_sign` call opened another approval window,