feat: Leads — Button zur erstellten Vorschau-Website

- Vorschau-Button (Auge, primary) je Lead -> previewUrl der deployten Website
- previewUrl live gejoint (Lead->Kunde per E-Mail->websiteProjects status deployed/ready); Preview haengt an anderem Repo als lead.repoUrl -> Kunden-Join
- attachWoids -> attachLeadLinks (haengt jetzt woid + previewUrl an)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/pages/LeadsPage.jsx

@@ -17,6 +17,7 @@ import {
   FaArrowsRotate,
   FaCheck,
   FaCopy,
+  FaEye,
   FaHashtag,
   FaTriangleExclamation,
 } from 'react-icons/fa6'
@@ -428,6 +429,11 @@ function LeadCard({ lead, pipeline, onUpdate }) {
             <FaGitAlt />
           </Button>
         )}
+        {lead.previewUrl && (
+          <Button size="sm" variant="primary" as="a" href={lead.previewUrl} target="_blank" rel="noreferrer" title="Erstellte Vorschau-Website öffnen (Login-geschützt)" aria-label="Vorschau öffnen">
+            <FaEye />
+          </Button>
+        )}
         {lead.woid && (
           <Button
             size="sm"