Migrate model preset (#7542)

- Introduce `openai_models` in `/core`
- Move `PRESETS` under it
- Move `ModelPreset`, `ModelUpgrade`, `ReasoningEffortPreset`,
`ReasoningEffortPreset`, and `ReasoningEffortPreset` to `protocol`
- Introduce `Op::ListModels` and `EventMsg::AvailableModels`

Next steps:
- migrate `app-server` and `tui` to use the introduced Operation

codex-rs/Cargo.lock

@@ -1117,12 +1117,10 @@ name = "codex-common"
 version = "0.0.0"
 dependencies = [
  "clap",
- "codex-app-server-protocol",
  "codex-core",
  "codex-lmstudio",
  "codex-ollama",
  "codex-protocol",
- "once_cell",
  "serde",
  "toml",
 ]