docs: initialize stub-service repo with ADR-001

Architecture Decision Record for a Go-based HTTP stub/mock service
(Mountebank alternative) with Web UI and LLM-powered config generation.

Covers: component architecture, technology choices (Go + chi + Templ/htmx
+ SQLite), API design, data model, deployment model.

README.md

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+# stub-service
+
+Go-based HTTP stub/mock service with Web UI and LLM-powered configuration generation.
+
+An alternative to [Mountebank](http://www.mbtest.org/) focused on simplicity, a modern web interface, and AI-assisted stub creation.
+
+## Status
+
+**Planning phase** — see [ADR-001](docs/adr/adr-001.md) for the architecture decision record.
+
+## Features (planned)
+
+- HTTP/HTTPS stub server with rich request matching (equals, contains, regex, JSONPath, XPath)
+- REST API for full CRUD management of imposters and stubs
+- Web UI for browsing, creating, and editing mock configurations
+- Real-time request log viewer
+- LLM integration for natural-language stub generation
+- Proxy mode with record/replay
+- Response templating via Go templates
+- File-based or embedded database persistence
+- Docker-ready deployment
+
+## License
+
+Internal use.