fix(spawn): use detached:true so children are immune to terminal SIGINT

Children now get their own process group. Terminal Ctrl+C only reaches
the parent, which then does orderly tree-kill while children are still
alive and the process tree is intact.

ts/classes.smartshell.ts

@@ -119,7 +119,7 @@ export class Smartshell {
       shell: false, // SECURITY: Never use shell with untrusted input
       cwd: process.cwd(),
       env: options.env || process.env,
-      detached: false,
+      detached: true, // Own process group — immune to terminal SIGINT, managed by smartexit
       signal: options.signal,
     });
 
@@ -342,7 +342,7 @@ export class Smartshell {
       shell: true,
       cwd: process.cwd(),
       env: options.env || process.env,
-      detached: false,
+      detached: true, // Own process group — immune to terminal SIGINT, managed by smartexit
       signal: options.signal,
     });