docs(readme): add Phenotype fork-context preamble (#528)

helios-cli ships OpenAI Codex CLI's README verbatim. Prepend a fork-context
section that:

- declares this as a Phenotype-org fork of openai/codex
- enumerates recent fork-specific patches (CVE bumps in codex-rs #525/#526,
  workspace deps fix #527, OSSF Scorecard #524, action SHA pinning #519-#521,
  VitePress deploy bootstrap #518)
- points downstream readers at PLAN.md and docs/contributing.md for
  Phenotype-specific context
- documents upstream tracking strategy

Upstream README is preserved verbatim below the preamble.

Author: KooshaPari

README.md

@@ -1,3 +1,30 @@
+<!-- PHENOTYPE FORK CONTEXT — see "About this fork" below -->
+
+## About this fork
+
+`KooshaPari/helios-cli` is a Phenotype-org fork of [OpenAI Codex CLI](https://github.com/openai/codex). The upstream README is preserved verbatim below; this preamble documents fork-specific divergence so downstream consumers can tell what is upstream behavior versus a Phenotype patch.
+
+**Why we fork:** Codex CLI is one of the agent backends wired into the Phenotype `thegent` dispatcher. We carry security and workspace fixes ahead of upstream merge cadence and ship them via this fork's tagged releases.
+
+**Recent Phenotype-specific changes:**
+
+- **#527 — `fix(workspace): declare 19 missing workspace dependencies`** — restores `cargo metadata`/`cargo build` resolution in `codex-rs/` after upstream workspace drift.
+- **#526 — `fix(deps): bump 10 HIGH CVEs in codex-rs`** — `aws-lc-sys`, `quinn-proto`, `rustls-webpki` upgrades; closes RUSTSEC advisories that upstream had not yet absorbed.
+- **#525 — `fix(workspace): unblock codex-rs cargo resolution`** — preparatory unblock for the CVE sweep.
+- **#524 / #523 / #522** — OpenSSF Scorecard workflow, `CODE_OF_CONDUCT.md`, `.github/FUNDING.yml` — Phenotype-org hygiene baseline.
+- **#519–#521** — pinned floating external GitHub Actions to commit SHAs across `stage-gates.yml`, `issue-labeler.yml`, `issue-deduplicator.yml`.
+- **#518** — bootstrapped a VitePress docs deploy workflow.
+
+**Where to find Phenotype-specific docs:**
+
+- Roadmap and fork strategy: [`PLAN.md`](./PLAN.md)
+- Phenotype contribution conventions: [`docs/contributing.md`](./docs/contributing.md) and the upstream `AGENTS.md` chain in `docs/agents_md.md`
+- Phenotype org context: [`KooshaPari/phenotype-infrakit`](https://github.com/KooshaPari/phenotype-infrakit) and the `thegent` dispatcher
+
+**Upstream tracking:** we periodically rebase or merge from `openai/codex@main`. Open a PR against this fork for Phenotype-specific changes; upstreamable fixes should also be PR'd to `openai/codex` directly.
+
+---
+
 <p align="center"><code>npm i -g @openai/codex</code><br />or <code>brew install --cask codex</code></p>
 <p align="center"><strong>Codex CLI</strong> is a coding agent from OpenAI that runs locally on your computer.
 <p align="center">