커스텀 nRF52840 보드용 DTM 추가(RTT, 전원, LED)

- LED 표시, 전원 홀드, 버튼 길게 누름으로 RF 테스트 중지, UART/RTT 빌드 타깃 정리

.gitignore

@@ -0,0 +1,63 @@
+# --- Keil µVision build outputs ---
+**/_build/
+*.axf
+*.hex
+*.bin
+*.elf
+*.map
+*.htm
+*.lnp
+*.sct
+*.dep
+*.d
+*.o
+*.crf
+*.lst
+*.iex
+*.tra
+*.fed
+*.i
+*.scvd
+*.__i
+*.build_log.htm
+
+# Keil user-specific (do not share)
+*.uvguix
+*.uvguix.*
+*.uvoptx
+
+# CMSIS-Pack / RTE generated
+**/RTE/
+
+# --- IAR Embedded Workbench ---
+**/settings/
+**/Debug/
+**/Release/
+*.pbd
+*.pbi
+*.xcl
+*.dbgdt
+*.dnx
+*.wsdt
+
+# --- Segger Embedded Studio ---
+*.emSession
+*.emProject.bak
+
+# --- Nordic / J-Link ---
+*.jlink
+
+# --- OS & editors ---
+.DS_Store
+Thumbs.db
+desktop.ini
+*.swp
+*~
+.vscode/
+.idea/
+
+# --- Secrets (never commit) ---
+.env
+*.pem
+*.key
+credentials.json