Add Firefox cookie import and stealth mode

- Firefox cookie importer: reads cookies.sqlite with WAL-safe copy,
  profile detection via profiles.ini, cross-platform paths, domain filtering
- Stealth mode: opt-in via launch(stealth: true), patches navigator.webdriver,
  plugins/mimeTypes, permissions API, WebGL renderer, iframe isolation,
  languages, plus realistic Safari UA and context hardening
- Import tool now accepts 'safari' | 'firefox' source
- STEALTH.md reference documentation
- Upgraded @types/node to v25 for node:sqlite support

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dist/types.d.ts

@@ -5,6 +5,7 @@ export interface BrowserOptions {
     fullscreen?: boolean;
     preview?: boolean;
     previewDelay?: number;
+    stealth?: boolean;
 }
 export interface ElementInfo {
     tag: string;
@@ -254,7 +255,7 @@ export interface EmulateCommand {
 }
 export interface ImportCommand {
     cmd: 'import';
-    source: 'safari';
+    source: 'safari' | 'firefox';
     domain?: string;
     profile?: string;
 }