New model: gpt-5.3-codex

## Event

- type: added
- model: gpt-5.3-codex

## Metadata

```yaml
available: false
reason: metadata lookup failed or model not listed
```

## Triage Evidence (fixed-string checks in `src/`)

```yaml
exact_mentions:
  - src/cli/constants.ts:4 (gpt-5.3-codex)
predecessor_mentions: []
```

## Decision

Changes appear to be required in `src/`.
