fix: image-ref Titel-Bug, CSP, ARIA-Labels, Onboarding i18n

- image-ref.js: .widget-title-text → .widget-title (Titel-Update war kaputt)
- Alle 3 Manifests: explizites content_security_policy (script-src/object-src 'self')
- i18n.js: applyLanguage() setzt aria-label synchron zu title
- newtab.html: 6 Close-Buttons + Search-Submit mit data-i18n-title
- i18n.js: 4 neue Keys (dialog.close, search.submit_title, onboarding.tradecenter_desc)
- onboarding.js: TradeCenter-Beschreibung auf t() umgestellt

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

manifest.opera.json

@@ -40,6 +40,9 @@
     "default_title": "Hellion Dashboard"
   },
 
+  "content_security_policy": {
+    "extension_pages": "script-src 'self'; object-src 'self'"
+  },
   "icons": {
     "16": "assets/icons/icon16.png",
     "48": "assets/icons/icon48.png",