feat: handle brave_search in API key test endpoint

Add a branch in test_key to route brave_search provider to
crate::services::brave_search::test_api_key instead of the LLM factory.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/handlers/api_keys.rs

@@ -121,6 +121,31 @@ pub async fn test_key(
     let decrypted_key =
         encryption::decrypt(&master_key, &stored_key.encrypted_key, &stored_key.nonce)?;
 
+    // Handle Brave Search key testing separately (not an LLM provider)
+    if provider == "brave_search" {
+        let result = crate::services::brave_search::test_api_key(
+            &state.http_client,
+            &decrypted_key,
+        ).await;
+
+        return match result {
+            Ok(()) => Ok(Json(TestResult {
+                success: true,
+                message: "Brave Search API key is valid and working".into(),
+            })),
+            Err(e) => {
+                let message = match &e {
+                    AppError::BadRequest(msg) => msg.clone(),
+                    _ => "Brave Search API key test failed.".into(),
+                };
+                Ok(Json(TestResult {
+                    success: false,
+                    message,
+                }))
+            }
+        };
+    }
+
     // Create a provider instance
     let llm_provider = factory::create_provider(&provider, decrypted_key)?;