fix(cli): lazy-load unified dashboard deps and harden start API

Agent-Logs-Url: https://github.com/MervinPraison/PraisonAI/sessions/b7840be5-04fc-4c1e-b680-e75ec7b1ca3f

Co-authored-by: MervinPraison <454862+MervinPraison@users.noreply.github.com>

Author: Copilot

src/praisonai/praisonai/cli/commands/unified.py

@@ -11,7 +11,7 @@
 import atexit
 import signal
 from pathlib import Path
-from typing import Dict, Set
+from typing import Set
 
 import typer
 
@@ -488,4 +488,4 @@ async def health():
         console.print("\n[yellow]🌟 Unified Dashboard stopped.[/yellow]")
     except Exception as e:
         console.print(f"[red]Error starting unified dashboard: {e}[/red]")
-        raise typer.Abort()
+        raise typer.Abort()