Add timesync burst handling and sender-only timeout

- Add TimeSync fault code and labels in UI/SD/web docs
- Trigger receiver beacon bursts on sender drift, but keep errors sender-local
- Sender flags TimeSync only after TIME_SYNC_ERROR_TIMEOUT_MS

include/data_model.h

@@ -6,7 +6,8 @@ enum class FaultType : uint8_t {
   None = 0,
   MeterRead = 1,
   Decode = 2,
-  LoraTx = 3
+  LoraTx = 3,
+  TimeSync = 4
 };
 
 struct FaultCounters {