Prototype a continuous integration workflow

This workflow is too spendthrift for deployment: every job sets up Rust,
and the `build` job also installs Trunk, which takes even more
resources. The workflow serves well, however, as a proof of concept.
Introducing a syntax error into `src/main.rs` causes the `build` and
`test` jobs to fail, but allows `run-examples` to succeed. Similarly,
introducing a syntax error into `examples/point-on-sphere.rs` causes
`run-examples` to fail, but allows the other jobs to succeed.

.forgejo/run-examples/action.yaml

@@ -0,0 +1,12 @@
+# run all Cargo examples, as described here:
+#
+#   Karol Kuczmarski. "Add examples to your Rust libraries"
+#   http://xion.io/post/code/rust-examples.html
+#
+runs:
+  using: "composite"
+  steps:
+    - run: cd app-proto; cargo run --example irisawa-hexlet
+    - run: cd app-proto; cargo run --example three-spheres
+    - run: cd app-proto; cargo run --example point-on-sphere
+    - run: cd app-proto; cargo run --example kaleidocycle

.forgejo/setup-rust/action.yaml

@@ -0,0 +1,10 @@
+# set up the Rust toolchain. based on David Tolnay's more general
+# `rust-toolchain` action for GitHub
+#
+#   https://github.com/dtolnay/rust-toolchain
+#
+runs:
+  using: "composite"
+  steps:
+    - run: curl --proto '=https' --tlsv1.2 --retry 10 --retry-connrefused --location --silent --show-error --fail 'https://sh.rustup.rs' | sh -s -- -y --profile minimal
+    - run: echo $HOME/.cargo/bin >> $GITHUB_PATH

.forgejo/workflows/continuous-integration.yaml

@@ -0,0 +1,25 @@
+on:
+  pull_request:
+  push:
+    branches: [main]
+jobs:
+  build:
+    runs-on: docker
+    steps:
+      - uses: https://code.forgejo.org/actions/checkout@v4
+      - uses: ./.forgejo/setup-rust
+      - run: rustup target add wasm32-unknown-unknown
+      - run: cargo install trunk
+      - run: cd app-proto; trunk build
+  test:
+    runs-on: docker
+    steps:
+      - uses: https://code.forgejo.org/actions/checkout@v4
+      - uses: ./.forgejo/setup-rust
+      - run: cd app-proto; cargo test
+  run-examples:
+    runs-on: docker
+    steps:
+      - uses: https://code.forgejo.org/actions/checkout@v4
+      - uses: ./.forgejo/setup-rust
+      - uses: ./.forgejo/run-examples