fix: make the home location lookup work against Claude

- Send the location question as a user message. A request with only a
  system message has no user content, which endpoints in front of Anthropic
  models reject ("text content blocks must be non-empty").
- Leave unknown fields out of the web search user_location. After a failed
  lookup there is no city or region, and the empty strings made every
  request fail ("user_location.city: String should have at least 1
  character").

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

custom_components/openai_compatible/config_flow.py

@@ -708,9 +708,11 @@ class OpenAISubentryFlowHandler(ConfigSubentryFlow):
             try:
                 response = await client.responses.create(
                     model=self.options.get(CONF_CHAT_MODEL, RECOMMENDED_CHAT_MODEL),
+                    # A user message, not a system one: endpoints in front of
+                    # Anthropic models reject a request without user content.
                     input=[
                         {
-                            "role": "system",
+                            "role": "user",
                             "content": "Where are the following coordinates located: "
                             f"({zone_home.attributes[EntityStateAttribute.LATITUDE]},"
                             f" {zone_home.attributes[EntityStateAttribute.LONGITUDE]})?",