Do the Trunk build check as an end-to-end test

This consolidates our whole CI workflow into `cargo test`.

.forgejo/workflows/continuous-integration.yaml

@@ -3,22 +3,11 @@ on:
   push:
     branches: [main]
 jobs:
-  # build the application, reporting success if there are no errors or warnings
-  build:
-    runs-on: docker
-    container:
-      image: cimg/rust:1.85-node
-    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
   # without warnings. the examples are run as tests, because we've configured
-  # each example target with `test = true` and `harness = false` in Cargo.toml
+  # 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:
@@ -28,4 +17,5 @@ jobs:
         working-directory: app-proto
     steps:
       - uses: https://code.forgejo.org/actions/checkout@v4
+      - uses: ./.forgejo/setup-trunk
       - run: RUSTFLAGS='-D warnings' cargo test