feat: show Config overview at start of exec (#1073)

Now the `exec` output starts with something like:

```
--------
workdir:  /Users/mbolin/code/codex/codex-rs
model:  o3
provider:  openai
approval:  Never
sandbox:  SandboxPolicy { permissions: [DiskFullReadAccess, DiskWritePlatformUserTempFolder, DiskWritePlatformGlobalTempFolder, DiskWriteCwd, DiskWriteFolder { folder: "/Users/mbolin/.pyenv/shims" }] }
--------
```

which makes it easier to reason about when looking at logs.

codex-rs/exec/src/lib.rs

@@ -18,6 +18,7 @@ use codex_core::protocol::SandboxPolicy;
 use codex_core::protocol::TaskCompleteEvent;
 use codex_core::util::is_inside_git_repo;
 use event_processor::EventProcessor;
+use event_processor::print_config_summary;
 use tracing::debug;
 use tracing::error;
 use tracing::info;
@@ -70,6 +71,8 @@ pub async fn run_main(cli: Cli) -> anyhow::Result<()> {
         model_provider: None,
     };
     let config = Config::load_with_overrides(overrides)?;
+    // Print the effective configuration so users can see what Codex is using.
+    print_config_summary(&config, stdout_with_ansi);
 
     if !skip_git_repo_check && !is_inside_git_repo(&config) {
         eprintln!("Not inside a Git repo and --skip-git-repo-check was not specified.");