style: cargo fmt — fix all formatting for CI

Ran cargo fmt across entire codebase to pass CI's cargo fmt --check.
No logic changes, only whitespace/formatting.

src/providers/traits.rs

@@ -2,12 +2,7 @@ use async_trait::async_trait;
 
 #[async_trait]
 pub trait Provider: Send + Sync {
-    async fn chat(
-        &self,
-        message: &str,
-        model: &str,
-        temperature: f64,
-    ) -> anyhow::Result<String> {
+    async fn chat(&self, message: &str, model: &str, temperature: f64) -> anyhow::Result<String> {
         self.chat_with_system(None, message, model, temperature)
             .await
     }