Add GraalPy 25 image replacing CPython

Multi-stage Dockerfile.graalpy on ghcr.io/graalvm/graalpy-community:25
that builds the granian and rloop PyO3 extensions from source against
GraalPy (no GraalPy wheels exist), installs the pure-Python deps, and
serves the unchanged RSGI app on the rloop event loop.

Adds docker-compose.graalpy.yml and a CI job publishing the image as
the *-graalpy tags on release/*.

README.md

@@ -16,6 +16,13 @@ over the RSGI protocol.
 
 No database, sessions, or authentication — the app is stateless.
 
+A second image runs the exact same app on [GraalPy](https://www.graalvm.org/python/)
+(GraalVM Community Edition 25) instead of CPython — see
+[Dockerfile.graalpy](Dockerfile.graalpy) and the
+[GraalPy image](#graalpy-image) section. Because GraalPy is not ABI-compatible
+with CPython wheels, the compiled `granian` and `rloop` extensions are built
+from source against GraalPy during the image build.
+
 ## Endpoints
 
 | Method | Path | Response |
@@ -62,6 +69,19 @@ docker compose up -d --build
 # App published at http://localhost:8080
 ```
 
+### GraalPy image
+
+An equivalent image based on `ghcr.io/graalvm/graalpy-community:25`
+(GraalPy 25.0.2 / Python 3.12.8) is available via a separate compose file:
+
+```bash
+docker compose -f docker-compose.graalpy.yml up -d --build
+# App published at http://localhost:8080
+```
+
+This image is published to the registry as the `*-graalpy` tags
+(e.g. `latest-graalpy`, `0.1.0-graalpy`).
+
 ### On the host
 
 ```bash
@@ -121,7 +141,15 @@ register handlers with `@app.GET(...)` decorators at import time —
 
 ## Deployment
 
-The `Dockerfile` is a multi-stage alpine build producing a minimal,
-non-root runtime image; pushing a `release/*` tag triggers the Gitea
-Actions workflow in `.gitea/workflows/build.yaml`, which builds and
-publishes the image to `gitea.woggioni.net/woggioni-opencode-agent/pyfconfig`.
+Two images are built from this repository:
+
+- `Dockerfile` — multi-stage alpine build on CPython, producing a minimal,
+  non-root runtime image.
+- `Dockerfile.graalpy` — multi-stage Oracle Linux build on GraalPy 25, where
+  the compiled `granian` and `rloop` extensions are compiled from source
+  against GraalPy (the Rust toolchain stays in the builder stage).
+
+Pushing a `release/*` tag triggers the Gitea Actions workflow in
+`.gitea/workflows/build.yaml`, which builds and publishes both images to
+`gitea.woggioni.net/woggioni/pyfconfig`: the CPython image as `latest` /
+`<version>`, and the GraalPy image as `latest-graalpy` / `<version>-graalpy`.