infra/docs: Docker Hub release pipeline, versioning, README overhaul

Reference prebuilt temetro/temetro-{backend,frontend} images in docker-compose
(with a build fallback) and stop baking the frontend API URL. Add a
tag-triggered GitHub Actions release workflow that pushes both images and cuts
a GitHub Release, plus RELEASING.md, CHANGELOG.md, and a root version. Overhaul
the root and frontend READMEs (screenshot, features, prebuilt-image quickstart,
LAN access, updating).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

RELEASING.md

@@ -0,0 +1,56 @@
+# Releasing temetro
+
+temetro is self-hosted: clinics run it with Docker and update by pulling new
+images. Each release publishes prebuilt images to Docker Hub and cuts a GitHub
+Release; the running app checks that release feed to tell admins an update is
+available. This document is the checklist for cutting one.
+
+## Versioning
+
+We follow [Semantic Versioning](https://semver.org/) — `MAJOR.MINOR.PATCH`,
+starting at **0.1.0**. The canonical version lives in the root
+[`package.json`](./package.json); `backend/package.json` and
+`frontend/package.json` track the same number. `GET /api/version` reports it.
+
+## One-time setup
+
+Add these repository secrets (GitHub → Settings → Secrets and variables →
+Actions) so the release workflow can publish:
+
+| Secret | What |
+| --- | --- |
+| `DOCKERHUB_USERNAME` | Docker Hub account with push access to the `temetro` namespace |
+| `DOCKERHUB_TOKEN` | A Docker Hub access token for that account |
+
+Images are published as `temetro/temetro-backend` and `temetro/temetro-frontend`.
+
+## Cutting a release
+
+1. **Bump the version** in `package.json`, `backend/package.json`, and
+   `frontend/package.json` to the new `X.Y.Z`.
+2. **Update [`CHANGELOG.md`](./CHANGELOG.md)**: move the `Unreleased` notes under a
+   new `## [X.Y.Z] — <date>` heading.
+3. **Commit** the bump (`chore(release): vX.Y.Z`).
+4. **Tag and push**:
+   ```bash
+   git tag vX.Y.Z
+   git push origin main --tags
+   ```
+5. The **`release` workflow** (`.github/workflows/release.yml`) then:
+   - builds and pushes both images tagged `X.Y.Z` **and** `latest`, and
+   - creates a **GitHub Release** with auto-generated notes.
+
+That GitHub Release is what the in-app update check compares against, so update
+notifications light up for everyone on an older version once it's published.
+
+## How clinics update
+
+On the server machine, from the directory holding `docker-compose.yml`:
+
+```bash
+docker compose pull && docker compose up -d
+```
+
+This pulls the new `latest` images and restarts. Pin a specific version with
+`TEMETRO_VERSION=X.Y.Z docker compose up -d`. Updating is optional — the in-app
+banner just makes it discoverable.