chore(core): change audio transcription job to use gemini 2.5 pro (#13202)

#### PR Dependency Tree


* **PR #13202** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

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

* **New Features**
* Improved the "Transcript audio" text action by updating its default AI
model to "gemini-2.5-pro" for enhanced performance.
* Enhanced audio transcription accuracy by refining audio content
handling with a more specific audio format.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: DarkSky <darksky2048@gmail.com>

packages/backend/server/src/__tests__/mocks/copilot.mock.ts

@@ -111,6 +111,19 @@ export class MockCopilotProvider extends OpenAIProvider {
         },
       ],
     },
+    {
+      id: 'gemini-2.5-pro',
+      capabilities: [
+        {
+          input: [ModelInputType.Text, ModelInputType.Image],
+          output: [
+            ModelOutputType.Text,
+            ModelOutputType.Object,
+            ModelOutputType.Structured,
+          ],
+        },
+      ],
+    },
   ];
 
   override async text(