feat(server): update claude models (#13677)

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

* **New Features**
* Copilot now defaults to the updated Claude Sonnet 4.5 model across
experiences for improved responses.

* **Chores**
* Consolidated available Anthropic models, removing older Sonnet 3.x
variants and standardizing Sonnet 4/4.5 options.
* Updated configuration defaults and schema mappings to reference the
new Sonnet 4.5 model.

* **Tests**
* Updated unit and end-to-end tests to reference the new model to ensure
consistent behavior.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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

@@ -55,7 +55,7 @@ defineModuleConfig('copilot', {
         embedding: 'gemini-embedding-001',
         image: 'gpt-image-1',
         rerank: 'gpt-4.1',
-        coding: 'claude-sonnet-4@20250514',
+        coding: 'claude-sonnet-4-5@20250929',
         complex_text_generation: 'gpt-4o-2024-08-06',
         quick_decision_making: 'gpt-5-mini',
         quick_text_generation: 'gemini-2.5-flash',