Add README.md files for web-app-bookwyrm, web-app-postmarks, and web-app-socialhome roles

Introduce integration test to ensure all web-app-* roles contain a README.md (required for Web App Desktop visibility)

See: https://chatgpt.com/share/68b6be49-7b78-800f-a3ff-bf922b4b083f

roles/web-app-bookwyrm/README.md

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+# BookWyrm
+
+## Description
+
+Host your own social reading platform with **BookWyrm**. This role deploys BookWyrm via Docker Compose, wires domains and ports, and offers optional OIDC integration so your readers can sign in through your central identity provider.
+
+## Overview
+
+This role provisions a BookWyrm application stack with Docker. It supports PostgreSQL and Redis, sets sensible environment defaults, and exposes an application container plus a dedicated Celery worker. A reverse proxy (provided elsewhere in your stack) fronts the service for public access.
+
+## Features
+
+- **Fully Dockerized Deployment:** Builds and runs BookWyrm containers (app + worker) using Docker Compose.
+- **Production-friendly Settings:** Environment templating for database, Redis, and security-relevant settings (e.g., `SECRET_KEY`).
+- **Optional OIDC:** Can integrate with your OIDC provider (e.g., Keycloak) directly or behind oauth2-proxy (depending on your flavor).
+- **Volumes for Data & Media:** Persistent volumes for BookWyrm data and media assets.
+- **Redis & Celery Worker:** Background tasks processed by Celery; Redis used for broker and cache.
+- **Desktop Integration Hooks:** Compatible with your Web App Desktop listing when the role includes this README.
+- **Matomo/CSS/Desktop Flags:** Standard feature flags are available for consistent theming/analytics across apps in your ecosystem.
+
+## Further Resources
+
+- [BookWyrm (GitHub)](https://github.com/bookwyrm-social/bookwyrm)
+- [BookWyrm Documentation](https://docs.joinbookwyrm.com/)
+- [OpenID Connect (Wikipedia)](https://en.wikipedia.org/wiki/OpenID_Connect)