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/profile_selector.rs

@@ -130,8 +130,8 @@ impl Render for ProfileSelector {
 
         let model_registry = LanguageModelRegistry::read_global(cx);
         let supports_tools = model_registry
-            .active_model()
-            .map_or(false, |model| model.supports_tools());
+            .default_model()
+            .map_or(false, |default| default.model.supports_tools());
 
         let icon = match profile_id.as_str() {
             "write" => IconName::Pencil,