docs: add dedicated Built with Okapi showcase page

docs/built-with-okapi.md

@@ -0,0 +1,46 @@
+---
+title: Built with Okapi
+layout: default
+nav_order: 8
+---
+
+# Built with Okapi
+
+A showcase of open-source projects using **Okapi** in production. If you've built something with Okapi, we'd love to feature it — see [Add your project](#add-your-project) below.
+
+---
+
+## Projects
+
+### [Posta](https://github.com/goposta/posta)
+
+Self-hosted email delivery platform. Send emails via an HTTP API with SMTP delivery, templates, storage, and analytics.
+
+- **Use case:** Transactional and marketing email
+- **Repository:** [github.com/goposta/posta](https://github.com/goposta/posta)
+
+### [Goma Admin](https://github.com/jkaninda/goma-admin)
+
+Control plane for [Goma Gateway](https://github.com/jkaninda/goma-gateway). Manage, configure, and monitor distributed API gateways from a unified dashboard.
+
+- **Use case:** API gateway management
+- **Repository:** [github.com/jkaninda/goma-admin](https://github.com/jkaninda/goma-admin)
+
+### [Miabi](https://github.com/miabi-io/miabi)
+
+Open-source, self-hosted PaaS. Deploy containerized apps from Git, Docker images, or templates with builds, domains, SSL, databases, backups, and monitoring built in.
+
+- **Use case:** Self-hosted application platform
+- **Repository:** [github.com/miabi-io/miabi](https://github.com/miabi-io/miabi)
+
+---
+
+## Add your project
+
+Using Okapi in an open-source project? Add it to this page:
+
+1. Fork the [okapi repository](https://github.com/jkaninda/okapi).
+2. Edit [`docs/built-with-okapi.md`](https://github.com/jkaninda/okapi/blob/main/docs/built-with-okapi.md) and add your project following the format above (name, one-line description, use case, repository link).
+3. Open a pull request.
+
+You can also [open an issue](https://github.com/jkaninda/okapi/issues) to suggest a project.