Use cargo-llvm-cov baked into the rust-ci image instead of caching

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.forgejo/workflows/ci.yml

@@ -101,14 +101,8 @@ jobs:
           restore-keys: |
             sccache-${{ runner.os }}-
 
-      # Not baked into the rust-ci image (see docker/rust-ci in
-      # infrastructure) — install fresh each run rather than bumping the
-      # shared image just for this one project.
-      - name: Install cargo-llvm-cov
-        run: |
-          rustup component add llvm-tools-preview
-          command -v cargo-llvm-cov >/dev/null 2>&1 || cargo install cargo-llvm-cov --locked
-
+      # cargo-llvm-cov and llvm-tools-preview are baked into the rust-ci
+      # image (see docker/rust-ci in infrastructure).
       # Reports coverage only — no --fail-under-lines yet. main.rs is
       # excluded: thin argv dispatch exercised by the real end-to-end
       # `cargo run`, not unit tests, so it's not a meaningful signal here.