ai: Separate model settings for each feature (#28088)

Closes: https://github.com/zed-industries/zed/issues/20582

Allows users to select a specific model for each AI-powered feature:
- Agent panel
- Inline assistant
- Thread summarization
- Commit message generation

If unspecified for a given feature, it will use the `default_model`
setting.

Release Notes:

- Added support for configuring a specific model for each AI-powered
feature

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>
Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>

crates/agent/src/message_editor.rs

@@ -1,5 +1,6 @@
 use std::sync::Arc;
 
+use crate::assistant_model_selector::ModelType;
 use collections::HashSet;
 use editor::actions::MoveUp;
 use editor::{ContextMenuOptions, ContextMenuPlacement, Editor, EditorElement, EditorStyle};
@@ -10,7 +11,7 @@ use gpui::{
     WeakEntity, linear_color_stop, linear_gradient, point,
 };
 use language::Buffer;
-use language_model::LanguageModelRegistry;
+use language_model::{ConfiguredModel, LanguageModelRegistry};
 use language_model_selector::ToggleModelSelector;
 use multi_buffer;
 use project::Project;
@@ -139,6 +140,7 @@ impl MessageEditor {
                     fs.clone(),
                     model_selector_menu_handle,
                     editor.focus_handle(cx),
+                    ModelType::Default,
                     window,
                     cx,
                 )
@@ -191,7 +193,7 @@ impl MessageEditor {
 
     fn is_model_selected(&self, cx: &App) -> bool {
         LanguageModelRegistry::read_global(cx)
-            .active_model()
+            .default_model()
             .is_some()
     }
 
@@ -201,20 +203,16 @@ impl MessageEditor {
         window: &mut Window,
         cx: &mut Context<Self>,
     ) {
-        let provider = LanguageModelRegistry::read_global(cx).active_provider();
-        if provider
-            .as_ref()
-            .map_or(false, |provider| provider.must_accept_terms(cx))
-        {
+        let model_registry = LanguageModelRegistry::read_global(cx);
+        let Some(ConfiguredModel { model, provider }) = model_registry.default_model() else {
+            return;
+        };
+
+        if provider.must_accept_terms(cx) {
             cx.notify();
             return;
         }
 
-        let model_registry = LanguageModelRegistry::read_global(cx);
-        let Some(model) = model_registry.active_model() else {
-            return;
-        };
-
         let user_message = self.editor.update(cx, |editor, cx| {
             let text = editor.text(cx);
             editor.clear(window, cx);