msp: add minimum power index to MSP_VTX_CONFIG

Adds minPowerIndex (byte 12) to MSP_VTX_CONFIG response to indicate
the minimum valid power index for the VTX device.

- MSP VTX: minPowerIndex = 0 (supports power off at index 0)
- SmartAudio/Tramp: minPowerIndex = 1 (power off not supported)

This allows configurator to correctly display all available power
levels without hardcoding device-specific logic.

Backward compatible: old configurators will ignore the extra byte.

Related: iNavFlight/inav-configurator#2486

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: sensei-hacker

.gitignore

@@ -46,3 +46,9 @@ launch.json
 # Assitnow token and files for test script
 tokens.yaml
 *.ubx
+
+# Local development files
+.semgrepignore
+build_sitl/
+CLAUDE.md
+brother/

src/main/fc/fc_msp.c

@@ -1526,6 +1526,12 @@ static bool mspFcProcessOutCommand(uint16_t cmdMSP, sbuf_t *dst, mspPostProcessF
                 sbufWriteU8(dst, vtxDevice->capability.bandCount);
                 sbufWriteU8(dst, vtxDevice->capability.channelCount);
                 sbufWriteU8(dst, vtxDevice->capability.powerCount);
+
+                uint8_t minPowerIndex = 1;
+                if (deviceType == VTXDEV_MSP) {
+                    minPowerIndex = 0;
+                }
+                sbufWriteU8(dst, minPowerIndex);
             }
             else {
                 sbufWriteU8(dst, VTXDEV_UNKNOWN); // no VTX configured