VesiScan BASIC origin: Piezo + IMU firmware initial code

- nRF52840 + SoftDevice S140 BLE firmware
- Piezo ultrasound TX driver (2MHz, 8ch MUX)
- ICM42670P IMU 6-axis driver
- Echo AFE chain (ADA2200 + ADC121S051)
- BLE NUS command parser (mpa/mpc/mdc/mec/maa/msp)
- FDS flash config storage
- pc_firm parser and ADC driver included

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pc_firm/.gitignore

@@ -0,0 +1,33 @@
+# Compiled binaries
+*.o
+*.hex
+*.bin
+*.elf
+*.map
+*.lst
+
+# Build directories
+_build/
+build/
+output/
+
+# IDE/Editor
+.vscode/
+*.swp
+*.swo
+*~
+
+# Segger/J-Link
+*.jlink
+
+# nRF specific
+*.zip
+sdk_config.h.bak
+
+# Windows
+Thumbs.db
+desktop.ini
+
+# Temporary files
+*.tmp
+*.bak