add 'get rtcclock' CLI command to report RTC source and current time

Returns the hardware RTC type (DS3231, RV3028, PCF8563, RX8130CE)
or 'internal' when no external module was detected, alongside the
current date and time in UTC. Useful for verifying that an external
RTC is active and providing correct time to the node.

src/MeshCore.h

@@ -92,6 +92,8 @@ public:
    */
   virtual void tick() { /* no op */}
 
+  virtual const char* getSourceName() const { return "internal"; }
+
   uint32_t getCurrentTimeUnique() {
     uint32_t t = getCurrentTime();
     if (t <= last_unique) {

src/helpers/AutoDiscoverRTCClock.cpp

@@ -61,6 +61,11 @@ void AutoDiscoverRTCClock::begin(TwoWire& wire) {
     MESH_DEBUG_PRINTLN("RX8130CE: Initialized");
   }
 
+  if (ds3231_success)       _source_name = "DS3231";
+  else if (rv3028_success)  _source_name = "RV3028";
+  else if (rtc_8563_success) _source_name = "PCF8563";
+  else if (rtc_8130_success) _source_name = "RX8130CE";
+
   _has_hw_rtc = ds3231_success || rv3028_success || rtc_8563_success || rtc_8130_success;
   if (_has_hw_rtc) {
     syncSystemClock();

src/helpers/AutoDiscoverRTCClock.h

@@ -12,12 +12,15 @@ class AutoDiscoverRTCClock : public mesh::RTCClock {
   mesh::RTCClock* _fallback;
   bool _has_hw_rtc;
   unsigned long _last_sync_ms;
+  const char* _source_name;
 
   bool i2c_probe(TwoWire& wire, uint8_t addr);
   void syncSystemClock();
 public:
   AutoDiscoverRTCClock(mesh::RTCClock& fallback)
-    : _fallback(&fallback), _has_hw_rtc(false), _last_sync_ms(0) { }
+    : _fallback(&fallback), _has_hw_rtc(false), _last_sync_ms(0), _source_name("internal") { }
+
+  const char* getSourceName() const override { return _source_name; }
 
   void begin(TwoWire& wire);
   uint32_t getCurrentTime() override;

src/helpers/CommonCLI.cpp

@@ -886,6 +886,13 @@ void CommonCLI::handleGetCmd(uint32_t sender_timestamp, char* command, char* rep
 #else
     strcpy(reply, "ERROR: Power management not supported");
 #endif
+  } else if (memcmp(config, "rtcclock", 8) == 0) {
+    uint32_t now = getRTCClock()->getCurrentTime();
+    DateTime dt = DateTime(now);
+    sprintf(reply, "> %s | %04d-%02d-%02d %02d:%02d:%02d UTC",
+            getRTCClock()->getSourceName(),
+            dt.year(), dt.month(), dt.day(),
+            dt.hour(), dt.minute(), dt.second());
   } else {
     sprintf(reply, "??: %s", config);
   }