Model metadata not found for Astra

### Before filing

- [x] I searched [open and closed issues](https://github.com/block/berd/issues?q=is%3Aissue) for duplicates.
- [x] I reproduced this on the [latest release](https://github.com/block/berd/releases).
- [x] This is one bug, not several bundled together.

### Closest existing issue

None found

### What's broken

Warning: Model metadata for gpt-6-astra not found. Defaulting to fallback metadata; this can degrade performance and cause issues.

{"type":"error","status":400,"error":{"type":"invalid_request_error","message":"The 'gpt-6-astra' model requires a newer version of Codex. Please upgrade to the latest app or CLI and try again."}}

### Steps to reproduce

1. Launch Berd
2. Select GPT Astra
3. Error message: Warning: Model metadata for gpt-6-astra not found. Defaulting to fallback metadata; this can degrade performance and cause issues.

{"type":"error","status":400,"error":{"type":"invalid_request_error","message":"The 'gpt-6-astra' model requires a newer version of Codex. Please upgrade to the latest app or CLI and try again."}}

### What you expected to happen

Astra shares output which works in Berd V 0.6.2

### What actually happened

Warning: Model metadata for gpt-6-astra not found. Defaulting to fallback metadata; this can degrade performance and cause issues.

{"type":"error","status":400,"error":{"type":"invalid_request_error","message":"The 'gpt-6-astra' model requires a newer version of Codex. Please upgrade to the latest app or CLI and try again."}}

### How often does it happen?

Every time — reliably reproducible

### Berd version

.0.6.3

### Operating system

macOS (Apple Silicon)

### Model and provider

GPT 6 Astra

### Relevant log output

```text
Warning: Model metadata for gpt-6-astra not found. Defaulting to fallback metadata; this can degrade performance and cause issues.

{"type":"error","status":400,"error":{"type":"invalid_request_error","message":"The 'gpt-6-astra' model requires a newer version of Codex. Please upgrade to the latest app or CLI and try again."}}
```

### Screenshots, recordings, or other context

_No response_

No source file, test, or entry point is named. Start by searching the Berd codebase for `gpt-6-astra` and the “Model metadata” warning, then trace GPT Astra selection in version 0.6.3. Done means selecting GPT Astra no longer produces the metadata warning or the Codex 400 error, while Astra output works as in 0.6.2.

Written by the indexing model from the issue text.