Add /models command for enabling/disabling Ctrl+P model cycling

- New /models command with toggle UI for each available model
- Changes persist to enabledModels in settings.json
- Updates take effect immediately for Ctrl+P cycling

packages/coding-agent/src/core/settings-manager.ts

@@ -447,6 +447,11 @@ export class SettingsManager {
 		return this.settings.enabledModels;
 	}
 
+	setEnabledModels(patterns: string[] | undefined): void {
+		this.globalSettings.enabledModels = patterns;
+		this.save();
+	}
+
 	getDoubleEscapeAction(): "branch" | "tree" {
 		return this.settings.doubleEscapeAction ?? "tree";
 	}