[client/management/signal/relay] Update go.mod to use Go 1.24.10 and upgrade x/crypto dependencies (#4828)

Upgrade Go toolchain and golang.org/x/* deps to 1.24.10, standardize GitHub Actions to derive Go version from go.mod and adjust checkout ordering, raise WASM size limit to 55 MB, update FreeBSD tarball and gomobile refs, fix a few format-string/logging calls, treat usernames ending with $ as system accounts, and add Windows tests.

client/ssh/testutil/user_helpers.go

@@ -72,7 +72,8 @@ func IsSystemAccount(username string) bool {
 			return true
 		}
 	}
-	return false
+
+	return strings.HasSuffix(username, "$")
 }
 
 // RegisterTestUserCleanup registers a test user for cleanup