README / docs refactor (#2724)

This PR cleans up the monolithic README by breaking it into a set
navigable pages under docs/ (install, getting started, configuration,
authentication, sandboxing and approvals, platform details, FAQ, ZDR,
contributing, license). The top‑level README is now more concise and
intuitive, (with corrected screenshots).

It also consolidates overlapping content from codex-rs/README.md into
the top‑level docs and updates links accordingly. The codex-rs README
remains in place for now as a pointer and for continuity.

Finally, added an extensive config reference table at the bottom of
docs/config.md.

---------

Co-authored-by: easong-openai <easong@openai.com>

docs/zdr.md

@@ -0,0 +1,15 @@
+## Zero data retention (ZDR) usage
+
+Codex CLI **does** support OpenAI organizations with [Zero Data Retention (ZDR)](https://platform.openai.com/docs/guides/your-data#zero-data-retention) enabled. If your OpenAI organization has Zero Data Retention enabled and you still encounter errors such as:
+
+```
+OpenAI rejected the request. Error details: Status: 400, Code: unsupported_parameter, Type: invalid_request_error, Message: 400 Previous response cannot be used for this organization due to Zero Data Retention.
+```
+
+Ensure you are running `codex` with `--config disable_response_storage=true` or add this line to `~/.codex/config.toml` to avoid specifying the command line option each time:
+
+```toml
+disable_response_storage = true
+```
+
+See [the configuration documentation on `disable_response_storage`](./config.md#disable_response_storage) for details.