Nest extraData by section for clearer embedding content

Homebox's location fields were flattened into single-purpose keys
(locationName/locationDescription), which gave EmbeddingService no
way to group related fields when rendering vector-store content.
extraData is now Map<String, Map<String, Object>>, letting
HomeboxItemClient express "location" as its own section; buildExtraData
renders each section as a header with indented fields instead of a flat
"Extradata: key: value" line.

backend/src/main/java/com/vaessl/app/homebox/HomeboxItemClient.java

@@ -1,6 +1,6 @@
 package com.vaessl.app.homebox;
 
-import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import org.springframework.data.domain.Page;
@@ -73,12 +73,18 @@ public class HomeboxItemClient {
             String description = i.description();
 
             HomeboxParent parent = i.parent();
-            Map<String, Object> extraData = new HashMap<>();
+            Map<String, Map<String, Object>> extraData = new LinkedHashMap<>();
+            Map<String, Object> locationData = new LinkedHashMap<>();
+
             if (parent.name() != null && !parent.name().isBlank()) {
-                extraData.put("locationName", parent.name());
+                locationData.put("name", parent.name());
             }
             if (parent.description() != null && !parent.description().isBlank()) {
-                extraData.put("locationDescription", parent.description());
+                locationData.put("description", parent.description());
+            }
+
+            if (locationData != null && !locationData.isEmpty()) {
+                extraData.put("location", locationData);
             }
 
             return new ServiceItem(id, title, description, extraData);