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-fonts.sh

@@ -18,7 +18,7 @@ fonts=(
 # Function to clone or update the NerdFonts repository
 clone_or_update_repo()
 {
-  if [ ! -d "$TMP_PATH" ]; then
+  if [[ ! -d "$TMP_PATH" ]]; then
     git clone --quiet --filter=blob:none --sparse --depth=1 "$GIT_REPO" "$TMP_PATH"
   fi