assistant: Set default provider to zed.dev (#16454)

Do NOT merge until tomorrow

Release Notes:

- N/A

---------

Co-authored-by: Thorsten <thorsten@zed.dev>

crates/assistant/src/assistant_settings.rs

@@ -543,8 +543,8 @@ mod tests {
             assert_eq!(
                 AssistantSettings::get_global(cx).default_model,
                 LanguageModelSelection {
-                    provider: "openai".into(),
-                    model: "gpt-4o".into(),
+                    provider: "zed.dev".into(),
+                    model: "claude-3-5-sonnet".into(),
                 }
             );
         });