pre-commit: fail on trailing whitespace

pre-commit

@@ -14,3 +14,19 @@ if [ "$should_run" = "yes" ]; then
 else
     echo "No relevant changes; skipping Tailwind build."
 fi
+
+# Check for trailing whitespace in staged files, fail if found
+
+git diff --cached --name-only --diff-filter=ACM | while IFS= read -r file; do
+    [ -f "$file" ] || continue
+
+    case "$file" in
+        *.py|*.js|*.ts|*.sh|*.md|*.txt|*.html|*.css)
+            if grep -qE '[[:space:]]+$' "$file"; then
+                echo "Commit aborted due to trailing whitespace."
+                echo "Fix it manually or use tools/strip-trailing-whitespace.sh"
+                exit 1
+            fi
+            ;;
+    esac
+done