Fix room/repeater/sensor silent message rejection when companion RTC diverges from app clock

Don't store the login timestamp in last_timestamp. Login uses the
companion's RTC while messages use the app's clock - when these diverge,
messages get silently rejected by the replay check (sender_timestamp <
last_timestamp). Login replay protection is already handled by hasSeen()
in the mesh layer.

Fixes #1551

examples/simple_repeater/MyMesh.cpp

@@ -117,7 +117,10 @@ uint8_t MyMesh::handleLoginReq(const mesh::Identity& sender, const uint8_t* secr
     }
 
     MESH_DEBUG_PRINTLN("Login success!");
-    client->last_timestamp = sender_timestamp;
+    // NOTE: don't update last_timestamp here - login uses companion RTC which may differ
+    // from the app clock used for messages. Mixing the two causes silent message rejection
+    // when the companion RTC runs ahead of the app clock (see #1551).
+    // Login replay protection is already handled by hasSeen() in the mesh layer.
     client->last_activity = getRTCClock()->getCurrentTime();
     client->permissions &= ~0x03;
     client->permissions |= perms;

examples/simple_room_server/MyMesh.cpp

@@ -321,7 +321,10 @@ void MyMesh::onAnonDataRecv(mesh::Packet *packet, const uint8_t *secret, const m
       }
 
       MESH_DEBUG_PRINTLN("Login success!");
-      client->last_timestamp = sender_timestamp;
+      // NOTE: don't update last_timestamp here - login uses companion RTC which may differ
+      // from the app clock used for messages. Mixing the two causes silent message rejection
+      // when the companion RTC runs ahead of the app clock (see #1551).
+      // Login replay protection is already handled by hasSeen() in the mesh layer.
       client->extra.room.sync_since = sender_sync_since;
       client->extra.room.pending_ack = 0;
       client->extra.room.push_failures = 0;

examples/simple_sensor/SensorMesh.cpp

@@ -352,7 +352,10 @@ uint8_t SensorMesh::handleLoginReq(const mesh::Identity& sender, const uint8_t*
     }
 
     MESH_DEBUG_PRINTLN("Login success!");
-    client->last_timestamp = sender_timestamp;
+    // NOTE: don't update last_timestamp here - login uses companion RTC which may differ
+    // from the app clock used for messages. Mixing the two causes silent message rejection
+    // when the companion RTC runs ahead of the app clock (see #1551).
+    // Login replay protection is already handled by hasSeen() in the mesh layer.
     client->last_activity = getRTCClock()->getCurrentTime();
     client->permissions |= PERM_ACL_ADMIN;
     memcpy(client->shared_secret, secret, PUB_KEY_SIZE);