fix(installer): make install.sh compatible with macOS bash 3.2

${value,,} is a bash-4 expansion; macOS ships bash 3.2, so install.sh
died with 'bad substitution' before doing anything on every default
mac shell. Caught by the PAP-14994 macos-14 e2e run.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/install.sh

@@ -66,7 +66,9 @@ parse_bool() {
   local name="$1"
   local value="${2:-}"
 
-  case "${value,,}" in
+  # ${value,,} requires bash 4; macOS ships bash 3.2, so lowercase portably.
+  value="$(printf '%s' "$value" | tr '[:upper:]' '[:lower:]')"
+  case "$value" in
     ""|0|false|no|off) printf '0' ;;
     1|true|yes|on) printf '1' ;;
     *) fail "$name must be one of: 1, 0, true, false, yes, no, on, off" ;;