build: Remove hardcoded Homebrew path for solaar in macOS script

The `create-macos-app.sh` script previously defaulted to a hardcoded Homebrew path for the `solaar` executable. This change removes the specific path, defaulting instead to `solaar`.

This modification makes the script more flexible and robust. It allows the system's `PATH` to resolve the location of the `solaar` binary, accommodating various installation methods beyond a fixed Homebrew directory. The explicit check for the executable's existence is also removed, as the script will now rely on the command being available in the shell's environment, which is a more standard approach.

tools/create-macos-app.sh

@@ -3,14 +3,9 @@
 set -euo pipefail
 
 APP_ROOT=${1:-/Applications/Solaar.app}
-SOLAR_PATH=${SOLAR_PATH:-/opt/homebrew/bin/solaar}
+SOLAR_PATH=${SOLAR_PATH:-solaar}
 ICON_SOURCE=${ICON_SOURCE:-share/solaar/icons/solaar.svg}
 
-if [[ ! -x "${SOLAR_PATH}" ]]; then
-    echo "Error: Unable to execute ${SOLAR_PATH}. Set SOLAR_PATH to the solaar binary." >&2
-    exit 1
-fi
-
 case "${APP_ROOT}" in
     ""|"/"|".")
         echo "Error: Refusing to create app bundle at unsafe location: \"${APP_ROOT}\"" >&2