feat: add preview tool — navigate + screenshot in one call with optional POST

New MCP tool `preview` combines goto + screenshot with viewport control.
Optionally POSTs result to any HTTP endpoint (e.g. HUD/visor) via previewUrl.

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@saiden/browse",
-  "version": "0.3.3",
+  "version": "0.4.0",
   "description": "Headless browser automation for Claude Code using Playwright WebKit",
   "type": "module",
   "main": "dist/index.js",