fix(cmd): nil-guard CLI when emitting system-prompt notice in quiet mode

SetupCLIForNonInteractive returns nil when --quiet is active, matching
the pre-existing nil checks elsewhere in the same block (e.g. the
buffered debug-message branch). Without this guard the new
'System Prompt loaded' notice panicked on quiet, non-interactive runs.

Discovered via tmux smoke test of the #25 fix.

cmd/root.go

@@ -811,7 +811,7 @@ func runNormalMode(ctx context.Context) error {
 		}
 
 		DisplayDebugConfig(cli, kitInstance, mcpConfig, parsedProvider)
-		if systemPromptLoadedMsg != "" {
+		if systemPromptLoadedMsg != "" && cli != nil {
 			cli.DisplayInfo(systemPromptLoadedMsg)
 		}
 	}