Add error trap to log failures to syslog

Added an error trap before 'set -e' to log script failures to syslog.
This will help identify where the script is failing during startup,
since the instances are terminating before any logs are written.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: ryan-williams

src/ec2_gha/templates/user-script.sh.templ

@@ -3,6 +3,9 @@
 logger "EC2-GHA: Starting userdata script"
 echo "EC2-GHA: Starting userdata script" >&2
 
+# Log any errors to syslog before exiting
+trap 'logger "EC2-GHA: Script failed at line $$LINENO with exit code $$?"' ERR
+
 set -e
 
 # Set up error handling and failsafe termination