feat: Add image upload for tea varieties

- Add image upload field to tea form with preview
- Add image property to tea data model
- Update addTea() to include image data (base64)
- Update openTeaModal() to display image when editing
- Display tea images on tea cards
- Add handleImageUpload() method for file processing
- Add migration for existing teas without image field
- Add CSS styles for image preview and display on cards
- Images stored as base64 in localStorage/Nextcloud

Co-authored-by: trevor1969 <trevor1969@users.noreply.github.com>

styles.css

@@ -1013,3 +1013,26 @@ header p {
     color: #FFD700;
     font-size: 1rem;
 }
+
+/* Image Upload Preview */
+.image-preview {
+    margin-top: 10px;
+}
+
+.image-preview img {
+    max-width: 150px;
+    max-height: 150px;
+    border-radius: var(--border-radius);
+    box-shadow: var(--box-shadow);
+    object-fit: cover;
+}
+
+/* Tea card image */
+.tea-image {
+    width: 60px;
+    height: 60px;
+    border-radius: var(--border-radius);
+    object-fit: cover;
+    box-shadow: var(--box-shadow);
+    margin-right: 10px;
+}