fix(shell): use [[ instead of [ for conditional tests

Replace single brackets with double brackets in bash conditional
expressions across 14 files (28 changes). All scripts use bash
shebangs so [[ is safe everywhere (SonarCloud rule shelldre:S7688).

scripts/install-composer.sh

@@ -14,7 +14,7 @@ EXPECTED_CHECKSUM="$(php -r 'copy("https://composer.github.io/installer.sig", "p
 php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
 ACTUAL_CHECKSUM="$(php -r "echo hash_file('sha384', 'composer-setup.php');")"
 
-if [ "$EXPECTED_CHECKSUM" != "$ACTUAL_CHECKSUM" ]; then
+if [[ "$EXPECTED_CHECKSUM" != "$ACTUAL_CHECKSUM" ]]; then
   echo >&2 'ERROR: Invalid installer checksum'
   rm composer-setup.php
   exit 1
@@ -23,7 +23,7 @@ fi
 php composer-setup.php --quiet
 RESULT=$?
 rm composer-setup.php
-if [ $RESULT -eq 0 ]; then
+if [[ $RESULT -eq 0 ]]; then
   mv composer.phar ~/.local/bin/composer
 fi
 exit $RESULT