Run CI on a stock image, installing Trunk by hand

Instead of building a custom CI image with Trunk pre-installed, let's
try running CI on a stock image, installing Trunk from a binary on every
workflow run.

.forgejo/workflows/continuous-integration.yaml

@@ -3,26 +3,17 @@ on:
   push:
     branches: [main]
 jobs:
-  # build and tag the Docker image that the rest of the jobs will run on
-  setup-image:
-    runs-on: self-hosted
-    defaults:
-      run:
-        working-directory: tools/ci-image
-    steps:
-      - uses: https://code.forgejo.org/actions/checkout@v4
-      - run: docker build . --tag dyna3:ci
   # build the application, reporting success if there are no errors or warnings
   build:
     runs-on: docker
     container:
-      image: dyna3:ci
-    needs: [setup-image]
+      image: rust:1.85-bookworm
     defaults:
       run:
         working-directory: app-proto
     steps:
       - uses: https://code.forgejo.org/actions/checkout@v4
+      - uses: ./.forgejo/setup-trunk
       - run: RUSTFLAGS='-D warnings' trunk build
   
   # run the automated tests, reporting success if the tests pass and were built
@@ -30,8 +21,7 @@ jobs:
   test:
     runs-on: docker
     container:
-      image: dyna3:ci
-    needs: [setup-image]
+      image: rust:1.85-bookworm
     defaults:
       run:
         working-directory: app-proto
@@ -48,8 +38,7 @@ jobs:
   run-examples:
     runs-on: docker
     container:
-      image: dyna3:ci
-    needs: [setup-image]
+      image: rust:1.85-bookworm
     defaults:
       run:
         working-directory: app-proto