feat: Avatar Scale (0.5×–3×) + Krea AI Bildgenerierung für Avatare

Backend:
- SessionRecord + AgentRecord: neues Feld AvatarScale (double, Default 1.0)
- DatabaseService: avatar_scale Migration, in Create/Update/GetWithStats
- SessionEndpoint + AgentEndpoint: avatarScale in Create/Update
- api.js: apiKreaStatus(), apiKreaGenerate()

Frontend:
- Session + Agent Templates: Range-Slider (0.5×–3×) in Avatar-Section
- Krea AI Generate: Prompt-Input + Magic-Button (nur wenn KreaToken konfiguriert)
- Live-Preview: transform: scale() auf Avatar-Vorschau
- Dashboard: scale() auf Session- und Agent-Card-Images
- form.css: avatar-scale-row + avatar-ai-section Styling

wwwroot/js/api.js

@@ -472,6 +472,27 @@ async function apiAdminImpersonate(userId) {
   return resp.json();
 }
 
+// ── Krea Image API ──
+
+async function apiKreaStatus() {
+  const resp = await fetch('/api/images/status');
+  if (!resp.ok) return { configured: false };
+  return resp.json();
+}
+
+async function apiKreaGenerate(prompt, model, width, height) {
+  const resp = await fetch('/api/images/generate', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ prompt, model: model || 'flux', width: width || 512, height: height || 512, batchSize: 1 })
+  });
+  if (!resp.ok) {
+    const err = await resp.json().catch(() => ({}));
+    throw new Error(err.error || 'Bildgenerierung fehlgeschlagen');
+  }
+  return resp.json();
+}
+
 // ── Backup API ──
 
 async function apiBackupDb() {