Add IN_433 regulatory region code

Append IN_433 as RegionCode 38 without renumbering existing values. This
prepares generated bindings and firmware support for India's 433.05-434.79 MHz
allocation under G.S.R. 347(E), 2022.

Regulatory source: https://eservices.dot.gov.in/sites/default/files/circular-notifications/the-use-of-low-power-radio-frequency-devices-in-the-frequency-band-433.05-to-434.79-mhz-exemption-from-license-rules-2022.pdf

Current DoT spectrum-plan context: https://www.dot.gov.in/static/uploads/2026/02/52e468605d5b63c6dfedcf538f1d7d36.pdf

Related firmware context: meshtastic/firmware#5940

Author: kholia

meshtastic/config.proto

@@ -990,6 +990,12 @@ message Config {
        * Check local law!
        */
       ITU2_125CM = 37;
+
+      /*
+       * India 433MHz
+       * G.S.R. 347(E), 2022
+       */
+      IN_433 = 38;
     }
 
     /*