fix: preserve newline character in project structure conversion

Command substitution ($()) strips trailing newlines, causing the
newline variable to be empty. This resulted in sed deleting all
\\n sequences instead of converting them to actual newlines.

Changed from:
  newline=$(printf '\n')  # Strips newline
To:
  printf -v newline '\n'  # Preserves newline

This fixes malformed project structure sections in generated agent
context files where directories should appear on separate lines.

Fixes issue where get_project_structure() output like
"backend/\\nfrontend/\\ntests/" was not properly converted to
multi-line format in agent files.

Author: carlo42

scripts/bash/update-agent-context.sh

@@ -347,7 +347,8 @@ create_new_agent_file() {
     done
 
     # Convert \n sequences to actual newlines
-    newline=$(printf '\n')
+    # Use printf -v to assign without command substitution (which strips trailing newlines)
+    printf -v newline '\n'
     sed -i.bak2 "s/\\\\n/${newline}/g" "$temp_file"
 
     # Clean up backup files