feat: Continuous integration via Forgejo Actions/runners (#75)

Adds a continuous integration workflow to the repository, using the [Forgejo Actions](https://forgejo.org/docs/next/user/actions/) framework.

Concurrently, Aaron added a [wiki page](https://code.studioinfinity.org/glen/dyna3/wiki/Continuous-integration) to document the continuous integration system. In particular, this page explains how to [run continuous integration checks on a development machine](wiki/Continuous-integration#execution), either directly or in a container.

Co-authored-by: Aaron Fenyes <aaron.fenyes@fareycircles.ooo>
Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Reviewed-on: StudioInfinity/dyna3#75
Co-authored-by: Vectornaut <vectornaut@nobody@nowhere.net>
Co-committed-by: Vectornaut <vectornaut@nobody@nowhere.net>

.forgejo/workflows/continuous-integration.yaml

@@ -0,0 +1,29 @@
+on:
+  pull_request:
+  push:
+    branches: [main]
+jobs:
+  # run the automated tests, reporting success if the tests pass and were built
+  # without warnings. the examples are run as tests, because we've configured
+  # each example target with `test = true` and `harness = false` in Cargo.toml.
+  # Trunk build failures caused by problems outside the Rust source code, like
+  # missing assets, should be caught by `trunk_build_test`
+  test:
+    runs-on: docker
+    container:
+      image: cimg/rust:1.85-node
+    defaults:
+      run:
+        # set the default working directory for each `run` step, relative to the
+        # workspace directory. this default only affects `run` steps (and if we
+        # tried to set the `working-directory` label for any other kind of step,
+        # it wouldn't be recognized anyway)
+        working-directory: app-proto
+    steps:
+      # Check out the repository so that its top-level directory is the
+      # workspace directory (action variable `github.workspace`, environment
+      # variable `$GITHUB_WORKSPACE`):
+      - uses: https://code.forgejo.org/actions/checkout@v4
+      
+      - uses: ./.forgejo/setup-trunk
+      - run: RUSTFLAGS='-D warnings' cargo test