feat: get prompt model names (#13607)

fix AI-419

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- New Features
- New API to fetch available models for a prompt, returning default,
optional, and pro models with human‑readable names.
- Added temperature and topP settings to prompt configuration for finer
control.
- Refactor
- When no model is chosen, the default model is used instead of
auto-picking a pro model.
- Model metadata across providers now includes readable names, improving
listings and selection UX.
- Tests
- Updated test snapshots and descriptions to reflect the new
default-model behavior.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/session.ts

@@ -130,15 +130,8 @@ export class ChatSession implements AsyncDisposable {
       paymentEnabled = false;
     }
 
-    if (paymentEnabled) {
-      if (isUserAIPro) {
-        if (!requestedModelId) {
-          const firstPro = this.proModels[0];
-          return normalize(firstPro);
-        }
-      } else if (isPro(requestedModelId)) {
-        return defaultModel;
-      }
+    if (paymentEnabled && !isUserAIPro && isPro(requestedModelId)) {
+      return defaultModel;
     }
 
     return normalize(requestedModelId);