Add shell check to pre-cmmit hooks & fix issues reported by it (#2579)

run_ui.sh

@@ -1,11 +1,11 @@
 #!/bin/bash
 
 pid=$(lsof -t -i :8080)
-if [ ! -z "$pid" ]; then
-  kill $pid
+if [ -n "$pid" ]; then
+  kill "$pid"
 fi
 
-cd skyvern-frontend
+cd skyvern-frontend || exit 1
 
 if [ ! -f .env ]; then
   cp .env.example .env