v1.7.1: GPS time sync, timezone picker, status bar clock

- GPS time sync via UBlox MIA-M10Q (38400 baud auto-detect)
- Custom zero-dependency NMEA parser with XOR checksum validation
- Only trust GPS time when satellites > 0 (no stale RTC cache)
- DST-aware timezone picker at first boot (21 cities, POSIX TZ strings)
- Timezone also configurable in Settings > GPS/Time
- GPS Time on by default, GPS Location off by default (opt-in)
- Status bar: clock (top-left), Ratspeak.org (center), battery (right)
- 12h time default (no AM/PM), configurable 24h in settings
- NVS persistence of GPS time for approximate timestamps across reboots
- Fix factory reset Enter key bleed-through (600ms input guard)
- Fix hardcoded UTC-5 NTP timezone (now uses DST-aware POSIX TZ)

src/hal/GPSManager.cpp

@@ -65,9 +65,15 @@ void GPSManager::loop() {
     NMEAData& d = _parser.data();
     if (d.timeUpdated) {
         d.timeUpdated = false;
-        _lastFixMs = millis();
-        if (d.timeValid && (millis() - _lastTimeSyncMs >= TIME_SYNC_INTERVAL_MS || _timeSyncCount == 0)) {
+        // Only trust GPS time when we have actual satellite lock (sats > 0).
+        // With sats=0 the module returns cached RTC time which drifts.
+        bool hasSatFix = (d.satellites > 0);
+        if (hasSatFix) _lastFixMs = millis();
+        if (d.timeValid && hasSatFix && (millis() - _lastTimeSyncMs >= TIME_SYNC_INTERVAL_MS || _timeSyncCount == 0)) {
             syncSystemTime();
+            // Persist time to NVS so reboots without WiFi/GPS have approximate time
+            persistToNVS();
+            _lastPersistMs = millis();
         }
     }
 
@@ -76,12 +82,6 @@ void GPSManager::loop() {
         d.locationUpdated = false;
         _locationValid = d.locationValid;
         _lastFixMs = millis();
-
-        // Periodic NVS persist
-        if (_locationValid && (millis() - _lastPersistMs >= PERSIST_INTERVAL_MS)) {
-            persistToNVS();
-            _lastPersistMs = millis();
-        }
     }
 
     // Stale fix detection
@@ -150,12 +150,8 @@ void GPSManager::syncSystemTime() {
     _lastTimeSyncMs = millis();
     _timeSyncCount++;
 
-    // Set TZ from utcOffset so localtime() works correctly
-    // POSIX TZ: "UTC<offset>" where offset sign is inverted
-    // e.g., UTC-5 (EST) → "UTC5" in POSIX notation
-    char tz[16];
-    snprintf(tz, sizeof(tz), "UTC%d", -_utcOffset);
-    setenv("TZ", tz, 1);
+    // Set TZ so localtime() returns correct local time (with DST if applicable)
+    setenv("TZ", _posixTZ, 1);
     tzset();
 
     Serial.printf("[GPS] System time synced: %04d-%02d-%02d %02d:%02d:%02d UTC (sync #%lu)\n",
@@ -177,9 +173,7 @@ void GPSManager::restoreTimeFromNVS() {
         settimeofday(&tv, nullptr);
 
         // Set TZ
-        char tz[16];
-        snprintf(tz, sizeof(tz), "UTC%d", -_utcOffset);
-        setenv("TZ", tz, 1);
+        setenv("TZ", _posixTZ, 1);
         tzset();
 
         time_t now = time(nullptr);
@@ -215,4 +209,9 @@ void GPSManager::persistToNVS() {
     prefs.end();
 }
 
+void GPSManager::setPosixTZ(const char* tz) {
+    strncpy(_posixTZ, tz, sizeof(_posixTZ) - 1);
+    _posixTZ[sizeof(_posixTZ) - 1] = '\0';
+}
+
 #endif // HAS_GPS