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

Do NOT merge until tomorrow

Release Notes:

- N/A

---------

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

assets/settings/default.json

@@ -395,9 +395,9 @@
     // The default model to use when creating new contexts.
     "default_model": {
       // The provider to use.
-      "provider": "openai",
+      "provider": "zed.dev",
       // The model to use.
-      "model": "gpt-4o"
+      "model": "claude-3-5-sonnet"
     }
   },
   // The settings for slash commands.

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(),
                 }
             );
         });