[radek-sixi]

Fixes #3482

Problem

Users reported in #3482 that rebooting a companion node (such as Heltec V4) after logging into a repeater prevents subsequent logins or post-login admin/status commands until the repeater itself is physically rebooted:

1. Companion RTC stepped backwards on reboot (BaseChatMesh::bootstrapRTCfromContacts()):
   On ESP32 boards (ESP32RTCClock::begin(), which restores _rtc_backup_time from RTC_NOINIT_ATTR) or boards with an external I2C RTC (AutoDiscoverRTCClock::begin()), the RTC clock already holds the current time on boot. However, MyMesh::begin() then calls bootstrapRTCfromContacts(), which unconditionally calls getRTCClock()->setCurrentTime(latest + 1) without checking whether latest >= getRTCClock()->getCurrentTime(). Because logging into a repeater and sending admin/status requests does not modify persisted contacts on flash, latest + 1 is older than the timestamps already sent to the repeater before the reboot, stepping the companion's RTC backwards (and overwriting _rtc_backup_time).
2. Inconsistent timestamp handling on blank-password (ACL) login (handleLoginReq / onAnonDataRecv):
   • When logging in with a password after the companion's clock stepped backwards, sender_timestamp <= client->last_timestamp rejects the login attempt (Failed to login).
   • When logging in with a blank password via ACL (data[0] == 0), client = acl.getClient(...) is non-NULL, which previously skipped the if (client == NULL) block entirely. As a result, handleLoginReq neither checked sender_timestamp <= client->last_timestamp nor updated client->last_timestamp and client->last_activity (and on Room Server also skipped updating sync_since, pending_ack, and push_failures). It returned RESP_SERVER_LOGIN_OK (so the UI reported being logged in as admin), while client->last_timestamp remained stuck at the pre-reboot value and caused onPeerDataRecv() to silently drop all subsequent status/clock-sync/CLI requests as replay attacks.

Fix

• In BaseChatMesh::bootstrapRTCfromContacts(), only advance the RTC clock to latest + 1 when latest >= getRTCClock()->getCurrentTime().
• In simple_repeater, simple_room_server, and simple_sensor, validate sender_timestamp > client->last_timestamp and update client->last_timestamp and client->last_activity (plus room sync state on simple_room_server) on both ACL (blank-password) and password login paths.