Add GPT-6.1 Terra to model catalogs (#57293)

## What changed

- Add `gpt-6.1-terra` to the bundled catalog and GCP Vertex model picker.
- Add `openai.gpt-6.1-terra` to Amazon Bedrock catalogs, including Global and US cross-region runtime variants.
- Use `gpt-6.1-terra` as GCP's preferred memory consolidation model.

## Testing

Extend catalog, model picker, thread startup, and Vertex request tests to cover GPT-6.1 Terra.

GitOrigin-RevId: edb3be3c4286c191349cdee742005ed3c67029e8

codex-rs/app-server/tests/suite/v2/thread_start.rs

@@ -246,6 +246,7 @@ async fn thread_start_provider_model_fallback_uses_bedrock_static_catalog() -> R
     .await?;
     for model in [
         "openai.gpt-6.1-sol",
+        "openai.gpt-6.1-terra",
         "openai.gpt-6-sol",
         "openai.gpt-6-luna",
         "openai.gpt-5.6-sol",
@@ -295,6 +296,8 @@ async fn thread_start_bedrock_runtime_prefers_global_cross_region_models() -> Re
     for model in [
         "global.openai.gpt-6.1-sol",
         "us.openai.gpt-6.1-sol",
+        "global.openai.gpt-6.1-terra",
+        "us.openai.gpt-6.1-terra",
         "global.openai.gpt-6-sol",
         "us.openai.gpt-6-sol",
         "global.openai.gpt-6-luna",