Add CI with checks and automated release builds

Gitea Actions workflow (.gitea/workflows/ci.yml):

- check job: ruff format --check, ruff check, ty check on pushes to main
- release job on v* tags: build a standalone Linux executable with
  PyInstaller (--onefile), smoke-test it, create a Gitea release via
  the API and upload the binary as an asset

Also add a pyinstaller build dependency group and bump to 0.3.0.

README.md

@@ -82,6 +82,21 @@ uv run ruff check src      # lint
 uv run ty check            # type check
 ```
 
+## CI / releases
+
+Gitea Actions (`.gitea/workflows/ci.yml`) runs two jobs:
+
+- **check** — format, lint, and type check on every push to `main`
+- **release** — on `v*` tags: builds a standalone Linux executable with
+  PyInstaller, smoke-tests it, creates a Gitea release, and uploads the
+  binary as an asset
+
+Cut a release with:
+
+```bash
+git tag vX.Y.Z && git push origin vX.Y.Z
+```
+
 ## Dependencies
 
 - **launchpadlib** — Launchpad REST API client