assistant2: Ensure errors are also displayed in populated new thread view (#27869)

Follow-up to https://github.com/zed-industries/zed/pull/27812

This PR makes sure these errors cases also show up in the panel's empty
state even when there is past data.

| No ToS | Missing Provider |
|--------|--------|
| ![CleanShot 2025-04-01 at 4  49
36@2x](https://github.com/user-attachments/assets/6da6bdc9-daa6-4a7b-a224-989eb845e205)
| ![CleanShot 2025-04-01 at 4  50
04@2x](https://github.com/user-attachments/assets/bddf62cb-3727-44b5-b115-9a88313c6d85)
|

Release Notes:

- N/A

crates/language_model/src/language_model.rs

@@ -353,7 +353,10 @@ pub trait LanguageModelProvider: 'static {
 
 #[derive(PartialEq, Eq)]
 pub enum LanguageModelProviderTosView {
-    ThreadEmptyState,
+    /// When there are some past interactions in the Agent Panel.
+    ThreadtEmptyState,
+    /// When there are no past interactions in the Agent Panel.
+    ThreadFreshStart,
     PromptEditorPopup,
     Configuration,
 }