ci: add forgejo checks workflow

AGENTS.md

@@ -44,6 +44,11 @@ Always run `./scripts/check_python_quality.sh` after making backend Python chang
 - Manual install is `~/.bun/bin/bun run hooks:install` from `frontend/` or `./scripts/install_git_hooks.sh` from the repo root
 - The `pre-commit` hook runs `./scripts/check_python_quality.sh` for staged backend changes and `./scripts/check_frontend_quality.sh` for staged frontend changes
 
+## CI
+
+- Forgejo CI lives in `.forgejo/workflows/ci.yml`
+- Pushes and pull requests run the same backend and frontend check scripts used locally
+
 ## Linting rules
 
 - Linter: Biome (config at `frontend/biome.json`)