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/prompt_library/src/prompt_library.rs

@@ -9,7 +9,7 @@ use gpui::{
 };
 use language::{Buffer, LanguageRegistry, language_settings::SoftWrap};
 use language_model::{
-    LanguageModelRegistry, LanguageModelRequest, LanguageModelRequestMessage, Role,
+    ConfiguredModel, LanguageModelRegistry, LanguageModelRequest, LanguageModelRequestMessage, Role,
 };
 use picker::{Picker, PickerDelegate};
 use release_channel::ReleaseChannel;
@@ -777,7 +777,9 @@ impl PromptLibrary {
         };
 
         let prompt_editor = &self.prompt_editors[&active_prompt_id].body_editor;
-        let Some(provider) = LanguageModelRegistry::read_global(cx).active_provider() else {
+        let Some(ConfiguredModel { provider, .. }) =
+            LanguageModelRegistry::read_global(cx).inline_assistant_model()
+        else {
             return;
         };
 
@@ -880,7 +882,9 @@ impl PromptLibrary {
     }
 
     fn count_tokens(&mut self, prompt_id: PromptId, window: &mut Window, cx: &mut Context<Self>) {
-        let Some(model) = LanguageModelRegistry::read_global(cx).active_model() else {
+        let Some(ConfiguredModel { model, .. }) =
+            LanguageModelRegistry::read_global(cx).default_model()
+        else {
             return;
         };
         if let Some(prompt) = self.prompt_editors.get_mut(&prompt_id) {
@@ -967,7 +971,9 @@ impl PromptLibrary {
                 let prompt_metadata = self.store.metadata(prompt_id)?;
                 let prompt_editor = &self.prompt_editors[&prompt_id];
                 let focus_handle = prompt_editor.body_editor.focus_handle(cx);
-                let model = LanguageModelRegistry::read_global(cx).active_model();
+                let model = LanguageModelRegistry::read_global(cx)
+                    .default_model()
+                    .map(|default| default.model);
                 let settings = ThemeSettings::get_global(cx);
 
                 Some(