feat(voyage): add Playwright + @axe-core/playwright devDependencies

Step 27 of v4.3 plan — adds Playwright 1.59.1 + axe-core/playwright 4.10.2
as devDependencies, npm script test:e2e, and playwright.config.mjs with
file:// baseURL pointing at playground/. Chromium browser binary installed
to ~/Library/Caches/ms-playwright/.

Trace: SC2 (WCAG verifikasjon krever browser-driver), research/04
Recommendation security; brief Constraint linje 64 (zero new deps i
playground/) er OK fordi Playwright er devDependency på voyage-plugin-rot,
ikke i playground/.

plugins/voyage/package.json

@@ -8,6 +8,7 @@
   },
   "scripts": {
     "test": "node --test 'tests/**/*.test.mjs'",
+    "test:e2e": "playwright test tests/e2e",
     "verify": "bash verify.sh"
   },
   "keywords": [
@@ -22,5 +23,9 @@
   "repository": {
     "type": "git",
     "url": "https://git.fromaitochitta.com/open/ktg-plugin-marketplace"
+  },
+  "devDependencies": {
+    "@axe-core/playwright": "^4.9.0",
+    "@playwright/test": "^1.44.0"
   }
 }