feat(network): a clear auth-failed node banner with a fix-it action

When the node rejects the wallet's RPC login (bad rpcuser/rpcpassword), the
status bar showed developer jargon ("Auth failed — check rpcuser/rpcpassword")
and the only action was Reconnect, which just repeats the failure. Now a
dedicated AuthFailed banner reason surfaces "Wallet can't sign in to the node"
with a plain-language detail and a real fix: Restart node for the embedded
daemon (regenerates its cookie creds) or Open config folder for an external one
(to fix DRAGONX.conf). Driven by a new rpc_auth_failed_ flag (set on the auth
path, cleared on each connect attempt), with evaluator unit tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.cpp

@@ -1553,7 +1553,7 @@ void I18n::loadBuiltinEnglish()
         strings_["sb_no_conf"] = "No DRAGONX.conf found";
         strings_["sb_starting_daemon"] = "Starting dragonxd...";
         strings_["sb_connecting_daemon"] = "Connecting to dragonxd...";
-        strings_["sb_auth_failed"] = "Auth failed — check rpcuser/rpcpassword";
+        strings_["sb_auth_failed"] = "Couldn't sign in to the node";
         strings_["sb_waiting_daemon"] = "Waiting for dragonxd to start...";
         strings_["sb_waiting_daemon_err"] = "Waiting for dragonxd — %s";
         strings_["sb_connecting_external"] = "Connecting to external daemon...";
@@ -1571,6 +1571,9 @@ void I18n::loadBuiltinEnglish()
         strings_["node_banner_lite_open_failed"] = "Couldn't open your wallet";
         strings_["node_banner_reconnect"] = "Reconnect";
         strings_["node_banner_restart"] = "Restart node";
+        strings_["node_banner_open_config"] = "Open config folder";
+        strings_["node_banner_auth_title"] = "Wallet can't sign in to the node";
+        strings_["node_banner_auth_detail"] = "The node rejected the wallet's saved login. Restart the node, or open the config folder to fix the login in DRAGONX.conf.";
         // Refresh-staleness badge (W6-2) on the Total Balance card.
         strings_["data_stale_prefix"] = "Updated";
         strings_["data_stale_tooltip"] =