docs: add README

README.md

@@ -0,0 +1,55 @@
+# mz-codes/.github
+
+This repository is the **organization-level `.github` repo** for the [`mz-codes`](https://github.com/mz-codes) GitHub organization. GitHub gives this special repository a privileged role: files placed here can act as defaults for every repository in the org, and the `profile/README.md` is rendered as the public org landing page.
+
+## Purpose
+
+The `.github` repo at the org level serves three jobs:
+
+1. **Public profile** — `profile/README.md` is shown on https://github.com/mz-codes as the org's public face.
+2. **Default community health files** — `CONTRIBUTING.md`, `SECURITY.md`, `SUPPORT.md`, `CODE_OF_CONDUCT.md`, `ISSUE_TEMPLATE/`, and `PULL_REQUEST_TEMPLATE.md` placed here are inherited by every repo in the org that does not define its own version.
+3. **Reusable workflows** — workflows under `.github/workflows/` can be referenced from any other `mz-codes` repo via `uses: mz-codes/.github/.github/workflows/<name>.yml@<ref>`.
+
+## Repository contents
+
+Current inventory:
+
+| Path | Purpose |
+| --- | --- |
+| `profile/README.md` | Public landing content rendered on the org page. |
+| `.github/workflows/ai-agent.yml` | Reusable workflow that runs `mz-codes/mz-ai-agent-action` on demand via `workflow_dispatch`. Accepts `provider`, `prompt`, `model`, `extra-options`, and `timeout-minutes`. Consumes the `AI_AGENT_CREDENTIALS` org secret. |
+| `README.md` | This file — documents the repo itself (not shown on the org profile). |
+
+> Note: only files under `profile/` feed the public org page. The root `README.md` is repo documentation for maintainers.
+
+## How files cascade across `mz-codes` repos
+
+GitHub's fallback rules apply per-file: if a consumer repo defines its own version, it wins; otherwise the org-level file is used. Reusable workflows are opt-in — a consumer repo must explicitly `uses:` them.
+
+```mermaid
+flowchart TD
+    A[mz-codes/.github] -->|profile/README.md| B[Public org page<br/>github.com/mz-codes]
+    A -->|community health files<br/>CONTRIBUTING, SECURITY, etc.| C{Consumer repo<br/>defines own?}
+    C -->|no| D[Inherits org default]
+    C -->|yes| E[Uses repo-local file]
+    A -->|.github/workflows/ai-agent.yml| F[Reusable workflow<br/>callable via 'uses:']
+    F --> G[mz-codes/repo-1]
+    F --> H[mz-codes/repo-2]
+    F --> I[mz-codes/repo-N]
+```
+
+## Adding a new shared file
+
+1. **Community health file** — drop it at the repo root (or under `.github/` / `profile/` per [GitHub's docs](https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions)). It applies automatically to repos that lack their own version.
+2. **Reusable workflow** — add it under `.github/workflows/` with `on: workflow_call` (or `workflow_dispatch` for manual runs), then reference it from consumer repos:
+   ```yaml
+   jobs:
+     run:
+       uses: mz-codes/.github/.github/workflows/ai-agent.yml@dev
+       secrets: inherit
+   ```
+3. **Profile change** — edit `profile/README.md`; the org page updates on push to the default branch.
+
+## Default branch
+
+The default branch is `dev`. Open PRs against `dev`; do not push directly.