Enable GPS time sync for Station G2 repeater builds

Add PERSISTANT_GPS and ENV_SKIP_GPS_DETECT flags to the Station G2
repeater build so the GPS module (when physically connected) is active
from boot and automatically syncs the RTC clock.

Without these flags, GPS detection fails on cold-starting GPS modules
that need more than 1 second to begin outputting NMEA data, causing all
GPS CLI commands to be unavailable. The existing MicroNMEALocationProvider
already handles initial sync after fix acquisition and periodic re-sync
every 30 minutes - these flags just ensure it is enabled.

Relates to #1426

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

variants/station_g2/platformio.ini

@@ -51,6 +51,8 @@ build_flags =
   -D ADVERT_LON=0.0
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
+  -D PERSISTANT_GPS=1
+  -D ENV_SKIP_GPS_DETECT=1
 ;  -D MESH_PACKET_LOGGING=1
 ;  -D MESH_DEBUG=1
 build_src_filter = ${Station_G2.build_src_filter}