feat(launcher): show rich panel suggesting /lc-new before handing off to Claude Code

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: aboucaud

src/lightcone/engine/launcher.py

@@ -615,6 +615,17 @@ def _exec_interactive(
     if os.environ.get("LIGHTCONE_LAUNCH_DEBUG"):
         _print(f"[lc launch debug] {' '.join(cmd)}")
 
+    from rich.panel import Panel
+
+    _console.print(
+        Panel(
+            "Run [bold cyan]/lc-new[/] to scaffold a new project and get started.",
+            title="[bold]lightcone sandbox[/]",
+            border_style="cyan",
+            expand=False,
+        )
+    )
+
     os.execvp(cmd[0], cmd)