fix: improve fnm retry delay and lock file cleanup

Author: draphy

install.sh

@@ -1873,7 +1873,7 @@ configure_fnm() {
             ((fnm_install_retries--))
             if [ $fnm_install_retries -gt 0 ]; then
                 print_warning "fnm download failed, retrying... ($fnm_install_retries attempts left)"
-                sleep 2
+                sleep 5
             fi
         done
 

update.sh

@@ -1162,9 +1162,10 @@ do_draphyos_update() {
         rm -f "$lock_file"
     fi
     echo $$ > "$lock_file"
-    # Clean up lock on function return (RETURN trap is function-scoped, doesn't conflict)
+    # Clean up lock on function return and script exit (belt-and-suspenders)
     _cleanup_draphyos_lock() { rm -f "$lock_file" 2>/dev/null || true; }
     trap '_cleanup_draphyos_lock' RETURN
+    trap '_cleanup_draphyos_lock; cleanup_sudo' EXIT INT TERM
 
     # Check for diff3 (required for three-way merge)
     if ! command -v diff3 &>/dev/null; then