Add image serving with CC license attribution

- S3 image proxy at /img/{path} with cache headers
- Species images displayed on species + cultivar detail pages
- Full CC attribution below each image: author, license, Wikimedia Commons link
- Image struct updated with source_url and license fields

herbapi-ui/assets/herbapi.css

@@ -1165,6 +1165,38 @@ td.placeholder {
     color: #e65100;
 }
 
+/* Species / cultivar images */
+
+.species-image-wrap {
+    margin: 1rem 0 0.5rem;
+}
+
+.species-image {
+    max-width: 360px;
+    max-height: 320px;
+    width: auto;
+    height: auto;
+    border-radius: var(--radius);
+    box-shadow: 0 2px 8px rgba(0,0,0,0.12);
+    object-fit: cover;
+}
+
+.image-attribution {
+    font-size: 0.75rem;
+    color: var(--text-muted);
+    margin-top: 0.35rem;
+    max-width: 360px;
+}
+
+.attribution-link {
+    color: var(--accent);
+    font-size: 0.75rem;
+}
+
+.attribution-link:hover {
+    text-decoration: underline;
+}
+
 /* Responsive */
 
 @media (max-width: 768px) {