docs: note GPLv3 scope and third-party licensing in README

Agentic Bridle's own source is GPLv3; crate dependencies and the integrated or
bundled services (Gitea, Gitea MCP, Kanboard, Qdrant, embedding server) keep
their own licenses and are not relicensed by this project.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019RZerbsHGF9Ka3bKhCjJ9m

README.md

@@ -1,2 +1,11 @@
 # Agentic-Bridle
 
+## License
+
+Agentic Bridle is licensed under the **GNU General Public License v3.0** — see [LICENSE](LICENSE).
+
+That covers this project's own source only. Everything else keeps its own license: Rust crate
+dependencies, and the services Bridle integrates with or bundles via Docker Compose — Gitea, the
+Gitea MCP server, Kanboard, Qdrant, and any embedding server — are each distributed under their
+respective terms and are **not** relicensed by this project. Check each component's own license
+before redistributing a deployment that includes them.