Fix install.sh and setup.sh for macOS compatibility

install.sh:
- Add SCRIPT_DIR so .env is written to the repo root regardless of cwd
- Detect OS (macOS/Linux) and show platform-appropriate missing-tool hints
- Check for Xcode Command Line Tools on macOS (required by IDF install.sh)
- Handle pip3 absence by falling back to python3 -m pip
- Remove ninja from hard prerequisite list (IDF bundles its own)

setup.sh:
- Show macOS serial port hint (/dev/cu.usbserial-*) vs Linux (/dev/ttyUSB0)
- Show macOS SD card mount hint (/Volumes/) vs Linux (/media/$USER/)

https://claude.ai/code/session_01MhAnh68DPNnTjcKqjNYDmk

setup.sh

@@ -82,7 +82,12 @@ prompt "Flash firmware to device now? [y/N] "
 read -r DO_FLASH
 
 if [[ "$DO_FLASH" =~ ^[Yy]$ ]]; then
-    prompt "Serial port (e.g. /dev/ttyUSB0, leave blank to auto-detect): "
+    if [[ "$(uname -s)" == "Darwin" ]]; then
+        PORT_HINT="/dev/cu.usbserial-* or /dev/cu.SLAB_USBtoUART"
+    else
+        PORT_HINT="/dev/ttyUSB0 or /dev/ttyACM0"
+    fi
+    prompt "Serial port (e.g. $PORT_HINT, leave blank to auto-detect): "
     read -r SERIAL_PORT
 
     if [[ -n "$SERIAL_PORT" ]]; then
@@ -96,7 +101,12 @@ fi
 
 heading "SD card setup"
 
-prompt "Mount path of SD card (e.g. /media/\$USER/KIDSBOX, leave blank to skip): "
+if [[ "$(uname -s)" == "Darwin" ]]; then
+    SD_HINT="/Volumes/KIDSBOX"
+else
+    SD_HINT="/media/\$USER/KIDSBOX"
+fi
+prompt "Mount path of SD card (e.g. $SD_HINT, leave blank to skip): "
 read -r SD_MOUNT
 
 if [[ -n "$SD_MOUNT" ]]; then