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

src/display_ui.cpp

@@ -172,6 +172,8 @@ static bool render_last_error_line(uint8_t y) {
     label = "decode";
   } else if (g_last_error == FaultType::LoraTx) {
     label = "lora";
+  } else if (g_last_error == FaultType::TimeSync) {
+    label = "timesync";
   }
   display.setCursor(0, y);
   display.printf("Err: %s %lus", label, static_cast<unsigned long>(age_seconds(g_last_error_ts, g_last_error_ms)));