Lock WebConfig logins per client address with a shared failure cap

/api/login locked every client for 30 s after five failures from anyone.
Anyone who could reach the login page could keep the owner locked out by
failing on purpose. If no login succeeded after a lockout, the lock also
returned from 2^31 to 2^32 ms (about 24.9 to 49.7 days) later, because the
deadline was never cleared and was compared as a signed difference.

Count failures per remote address instead. Five failures lock that address
for 30 s, as before. A shared budget caps failures from all addresses
together, so changing address does not add guesses: it holds six failures
and refills one every 6 s, the old global rate, so one failing address can
never empty it on its own. While it is empty every client waits, as before.
Lock times are measured as elapsed time.

The policy is a pure header, WebConfigLoginThrottle.h.
test_webconfig_login_throttle.py runs it directly (isolation, boundaries,
one-hour rate bounds, millis() half-wrap, saturation, eviction) and runs the
real handleLogin with ArduinoJson under ASan/UBSan. Putting every client on
one key, as the old code did, fails the handler test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/run-unit-tests.yml

@@ -629,6 +629,7 @@ jobs:
           python3 -B test/test_wifi_ota_start.py -v
           python3 -B test/test_webconfig_ap_start.py -v
           python3 -B test/test_webconfig_recovery_auth.py -v
+          python3 -B test/test_webconfig_login_throttle.py -v
           python3 -B test/test_esp32_wifi_scan_fix.py -v
           python3 -B test/test_esp32_wifi_scan_recipes.py -v