CI: migrate to bread-ecosystem's shared Arch build image

Routes the release build/test steps and a new fast pre-release
check.yml through ci/build.sh, which delegates to bread-ecosystem's
pinned shared Containerfile/build.sh instead of building against
whatever the bare hestia runner happens to have installed. Follows
the pattern already proven in breadpad. No extra ci/deps.txt: bread's
system_deps (systemd-libs, openssl, zlib) are all already pulled in
transitively by the shared image's base + git packages.

.forgejo/workflows/dev-release.yml

@@ -26,10 +26,10 @@ jobs:
         run: cd src && cargo run -p xtask --locked -- check-docs
 
       - name: build
-        run: cd src && cargo build --release --locked
+        run: cd src && bash ci/build.sh cargo build --release --locked
 
       - name: test
-        run: cd src && cargo test --release --locked --workspace
+        run: cd src && bash ci/build.sh cargo test --release --locked --workspace
 
       # breadd/Cargo.toml is the canonical version source (this workspace has
       # no shared workspace.package.version — breadd and bread-cli are kept