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/mcp-server/src/codex_tool_runner.rs

@@ -307,6 +307,7 @@ async fn run_codex_tool_session_inner(
                     | EventMsg::UndoCompleted(_)
                     | EventMsg::ExitedReviewMode(_)
                     | EventMsg::ContextCompacted(_)
+                    | EventMsg::ListModelsResponse(_)
                     | EventMsg::DeprecationNotice(_) => {
                         // For now, we do not do anything extra for these
                         // events. Note that