Plugin: self-hosted auto-updates from Gitea via PUC (hc-8gb)

Vendors YahnisElsts/plugin-update-checker v5.7 under vendor/ and wires it
to poll updates.json on the repo main branch. WP surfaces new versions
via Dashboard → Updates on its normal twice-daily cadence.

PUC is vendored (not a submodule) so Gitea's archive/main.zip — the
download target — includes it. Folder rename on install is handled by
PUC's built-in upgrader_source_selection filter.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -50,7 +50,26 @@ Phase 1 (this) is a checklist + Markdown report. Phase 3 will add per-step autom
 
 ## Distribution
 
-Internal/agency tool — not a WP.org plugin (decision `hc-5ix.26`). Distributed as a built ZIP. A self-hosted update channel is `hc-5ix.27` on the phase-3 backlog.
+Internal/agency tool — not a WP.org plugin (decision `hc-5ix.26`). Installed sites auto-update from Gitea via [Plugin Update Checker](https://github.com/YahnisElsts/plugin-update-checker) (vendored under `vendor/plugin-update-checker/`). PUC polls `updates.json` on the repo's main branch twice a day; new versions appear in *Dashboard → Updates*.
+
+### Releasing a new version
+
+1. Bump `Version:` in the `att-site-healthcheck.php` header **and** `ATT_HC_VERSION`.
+2. Bump `version` and `last_updated` in `updates.json`.
+3. Commit + push to `main`.
+
+Installed sites pick it up on their next update check (or immediately if an admin clicks *Check again* on the Updates screen). The `download_url` points at `archive/main.zip`, so whatever's on `main` at fetch time is what gets installed.
+
+### Updating PUC itself
+
+PUC is a vendored copy, not a submodule (so Gitea's `archive/main.zip` includes it). To update:
+
+```sh
+cd /tmp && git clone --depth 1 https://github.com/YahnisElsts/plugin-update-checker.git puc-new
+rm -rf vendor/plugin-update-checker
+cp -R /tmp/puc-new vendor/plugin-update-checker
+rm -rf vendor/plugin-update-checker/{.git,.github,build,vendor,examples,composer.json,phpcs.xml}
+```
 
 ## Tracking