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/browser.d.ts

@@ -13,6 +13,13 @@ export declare class ClaudeBrowser {
     private interceptPatterns;
     constructor(options?: BrowserOptions);
     launch(): Promise<void>;
+    /**
+     * Apply stealth patches via addInitScript.
+     * These run before any page script in all Playwright engines (WebKit included).
+     * Scripts are passed as strings since they execute in browser context, not Node.
+     * See STEALTH.md for full documentation.
+     */
+    private applyStealthPatches;
     private enterFullscreen;
     private previewAction;
     private setupErrorListener;