fix: build on the rust runner, because fedora-44's pnpm cannot start

The first run of this workflow failed before it did anything:

    pnpm: error while loading shared libraries: libatomic.so.1:
    cannot open shared object file: No such file or directory
    ##[error]Process completed with exit code 127.

`@pnpm/exe` is a native binary and the fedora-4x runner images lack libatomic,
so the pnpm they advertise (gitea-runners.md §4) cannot run at all.
`runner-rust` is built on `runner-fedora-44` and adds gcc, musl-gcc and cmake,
which pull libatomic in as a side effect — which is why blackbeard.observer has
been building its SPA there without hitting this.

A workaround, not the fix. The fix is libatomic in the fedora-4x Containerfiles,
per gitea-runners.md §5 — bake build dependencies into the image, not the
workflow — and this should move back when that lands: a 4 CPU / 4 GiB image to
run `vite build` is more than this needs.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012uDUodEcRbBwNRi3UCmw8f

.gitea/workflows/deploy.yaml

@@ -28,9 +28,23 @@ env:
 
 jobs:
   build:
-    # fedora-44 carries node + npm + pnpm (gitea-runners.md §4) and nothing else
-    # is needed — there is no Rust half here.
-    runs-on: fedora-44
+    # `rust`, not `fedora-44`, despite there being no Rust here.
+    #
+    # The fedora-4x images list pnpm (gitea-runners.md §4) but their pnpm cannot
+    # run: `@pnpm/exe` is a native binary and the images lack libatomic, so the
+    # very first step dies with
+    #
+    #   pnpm: error while loading shared libraries: libatomic.so.1
+    #
+    # `runner-rust` is built on `runner-fedora-44` and adds gcc, musl-gcc and
+    # cmake, which pull libatomic in as a side effect — which is why
+    # blackbeard.observer builds its SPA there and this one now does too.
+    #
+    # This is a workaround for a runner-image bug, not the fix. The fix is
+    # libatomic in the fedora-4x Containerfiles (gitea-runners.md §5: bake build
+    # dependencies into the image, not the workflow). Move back when that lands;
+    # a 4 CPU / 4 GiB image to run `vite build` is more than this needs.
+    runs-on: rust
     steps:
       - uses: actions/checkout@v4