refactor: rename rak_4631 to rak_wisblock_4631, add proper display names

Board naming now follows MeshCore conventions:
- rak_4631 → rak_wisblock_4631 (feature, file, Justfile, splash screen)
- Display splash shows human-readable names: "RAK WisBlock 4631",
  "Heltec v3", "Heltec v4"

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

Justfile

@@ -5,12 +5,12 @@ set shell := ["bash", "-c"]
 # check-all gracefully skips boards whose toolchain isn't installed.
 heltec_v3 := "heltec_v3 xtensa-esp32s3-none-elf esp32s3"
 heltec_v4 := "heltec_v4 xtensa-esp32s3-none-elf esp32s3"
-rak_4631  := "rak_4631 thumbv7em-none-eabihf nRF52840_xxAA"
+rak_wisblock_4631  := "rak_wisblock_4631 thumbv7em-none-eabihf nRF52840_xxAA"
 
 firmware_dir := "firmware"
 
 # All known boards
-boards := "heltec_v3 heltec_v4 rak_4631"
+boards := "heltec_v3 heltec_v4 rak_wisblock_4631"
 
 # Check all boards that can build with the available toolchain
 check-all:
@@ -81,5 +81,5 @@ _copy_firmware board profile:
 _info name:
     @if [ "{{name}}" == "heltec_v3" ]; then echo "{{heltec_v3}}"; \
      elif [ "{{name}}" == "heltec_v4" ]; then echo "{{heltec_v4}}"; \
-     elif [ "{{name}}" == "rak_4631" ]; then echo "{{rak_4631}}"; \
+     elif [ "{{name}}" == "rak_wisblock_4631" ]; then echo "{{rak_wisblock_4631}}"; \
      else echo "Unknown board: {{name}}" >&2; exit 1; fi