[config] Onboarding flow with persistence (#1929)

## Summary
In collaboration with @gpeal: upgrade the onboarding flow, and persist
user settings.

---------

Co-authored-by: Gabriel Peal <gabriel@openai.com>

codex-rs/Cargo.lock

@@ -708,6 +708,7 @@ dependencies = [
  "tokio-test",
  "tokio-util",
  "toml 0.9.4",
+ "toml_edit 0.23.3",
  "tracing",
  "tree-sitter",
  "tree-sitter-bash",
@@ -3273,7 +3274,7 @@ version = "3.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "edce586971a4dfaa28950c6f18ed55e0406c1ab88bbce2c6f6293a7aaba73d35"
 dependencies = [
- "toml_edit",
+ "toml_edit 0.22.27",
 ]
 
 [[package]]
@@ -4800,7 +4801,7 @@ dependencies = [
  "serde",
  "serde_spanned 0.6.9",
  "toml_datetime 0.6.11",
- "toml_edit",
+ "toml_edit 0.22.27",
 ]
 
 [[package]]
@@ -4850,10 +4851,23 @@ dependencies = [
 ]
 
 [[package]]
-name = "toml_parser"
-version = "1.0.1"
+name = "toml_edit"
+version = "0.23.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "97200572db069e74c512a14117b296ba0a80a30123fbbb5aa1f4a348f639ca30"
+checksum = "17d3b47e6b7a040216ae5302712c94d1cf88c95b47efa80e2c59ce96c878267e"
+dependencies = [
+ "indexmap 2.10.0",
+ "toml_datetime 0.7.0",
+ "toml_parser",
+ "toml_writer",
+ "winnow",
+]
+
+[[package]]
+name = "toml_parser"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b551886f449aa90d4fe2bdaa9f4a2577ad2dde302c61ecf262d80b116db95c10"
 dependencies = [
  "winnow",
 ]