feat(JUVENILE-AVATARS): Foto-Avatare pro Jungtier im Wurf-Detail

- JuvenileCard-Komponente in WurfDetailPage mit 36px-Kreis-Avatar links
- Fallback auf GerbilIcon (SVG-Silhouette) wenn kein profilePhotoUrl
- URL-basiertes Fehler-Tracking (failedUrl) statt useEffect+imgError
- wuerfe.css: Flex-Layout fuer Card+Avatar, overflow:hidden/object-fit:cover
- StammbaumPage: gleiche Lint-Verletzung (react-hooks/set-state-in-effect)
  behoben (failedUrl-Pattern, kein useEffect mehr fuer Bild-Reset)
- E2E: profilePhotoUrl auf Pippa (pup-abgabe), neuer Avatar-Test

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

gerbil-manager-web/src/pages/StammbaumPage.tsx

@@ -381,14 +381,13 @@ function PedigreeCard({
   const g = node.gerbil
   const chip = farbschlag ? chipColorFor(farbschlag) : null
   const dob = g.dateOfBirth ? formatDate(g.dateOfBirth) : null
-  const [imgError, setImgError] = useState(false)
-  useEffect(() => setImgError(false), [g.id])
-  const photoUrl =
-    !imgError && g.profilePhotoUrl
-      ? /^(https?:|data:|\/\/)/.test(g.profilePhotoUrl)
-        ? g.profilePhotoUrl
-        : `${API_BASE_URL}${g.profilePhotoUrl}`
-      : null
+  const [failedUrl, setFailedUrl] = useState<string | null>(null)
+  const rawUrl = g.profilePhotoUrl
+    ? /^(https?:|data:|\/\/)/.test(g.profilePhotoUrl)
+      ? g.profilePhotoUrl
+      : `${API_BASE_URL}${g.profilePhotoUrl}`
+    : null
+  const photoUrl = rawUrl !== failedUrl ? rawUrl : null
   return (
     <div
       className={isRoot ? 'pedigree-card pedigree-card--root' : 'pedigree-card'}
@@ -402,7 +401,7 @@ function PedigreeCard({
             src={photoUrl}
             alt={g.name || ''}
             className="pedigree-card__avatar"
-            onError={() => setImgError(true)}
+            onError={() => setFailedUrl(rawUrl)}
           />
         ) : (
           <GerbilIcon size="1.6rem" aria-hidden="true" />