Explicitly initialize gpsState.hwVersion to 0 in gpsInit()

Addresses Qodo code review suggestion to prevent sending uninitialized
memory over MSP_GPSSTATISTICS.

While global variables are zero-initialized in C, explicit initialization
is better practice:
- Makes intent clear in code
- Works for all GPS providers (UBLOX, MSP, FAKE)
- Future-proof if gpsState becomes non-global
- Documents that 0 means UNKNOWN

u-blox driver also initializes to UBX_HW_VERSION_UNKNOWN (0) during
configuration, but this ensures all code paths are safe.

Author: sensei-hacker

src/main/io/gps.c

@@ -451,6 +451,9 @@ void gpsInit(void)
     gpsStats.errors = 0;
     gpsStats.timeouts = 0;
 
+    // Initialize hardware version to unknown (for MSP_GPSSTATISTICS)
+    gpsState.hwVersion = 0;
+
     // Reset solution, timeout and prepare to start
     gpsResetSolution(&gpsSolDRV);
     gpsResetSolution(&gpsSol);