Initial: Angie 1.11.3 OCI image build for aarch64

Builds via dockerTools.streamLayeredImage from nixpkgs unstable's
pkgs.angie. Woodpecker pipeline pushes to git.oleks.space/oleks/angie
with both <version>-arm64 and latest-arm64 tags. Used by the
kotkanagrilli.fi staging Helm chart on the kotkan node (arm64) to
replace the upstream amd64-only runalsh/angie image.

README.md

@@ -0,0 +1,28 @@
+# angie-arm64
+
+OCI image for [Angie](https://angie.software/) (an nginx fork) on aarch64.
+Upstream `runalsh/angie` only publishes amd64 images, so we rebuild from the
+`pkgs.angie` package in nixpkgs and push the result to the private Gitea
+registry.
+
+## Output
+
+| Tag | Pushed when |
+|---|---|
+| `git.oleks.space/oleks/angie:<version>-arm64` | every successful CI run |
+| `git.oleks.space/oleks/angie:latest-arm64` | every successful CI run |
+
+The version string comes from `pkgs.angie.version` in nixpkgs unstable; bump
+the flake input to roll it forward.
+
+## Build locally
+
+```bash
+nix build .#default
+./result | skopeo copy docker-archive:/dev/stdin oci-archive:angie.tar
+```
+
+## Trigger CI
+
+Push to `main`/`master` or push a `v*` tag in the corresponding Gitea repo
+(`oleks/angie-arm64` — match the directory name when seeding it).