test(harness): name the root check for what it asserts, and lint the crate

`open_and_refresh_see_an_empty_origin_root` claimed more than it checked:
since the previous commit an empty *entry* is not a document, so `list`
being empty means "no documents", not "no entries". A check whose name
overstates it is the shape this repo keeps finding — a green tick against a
claim nobody verified. Renamed, and `wipe`'s doc now says out loud that it
cannot clear a zero-byte entry, and why that costs nothing.

`harness/opfs-contract` is not a workspace member, so the `test` job's
workspace-wide `cargo fmt --check` and clippy never reach it. The browser
job now runs both against it — it was, in fact, unformatted.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -107,6 +107,13 @@ jobs:
           curl -sSfL "$url" | tar -xz --strip-components=1 -C /usr/local/bin \
             "wasm-pack-${WASM_PACK_VERSION}-x86_64-unknown-linux-musl/wasm-pack"
           wasm-pack --version
+      # Not a workspace member (it only builds for wasm32), so the `test` job's
+      # workspace-wide fmt and clippy do not reach it.
+      - name: Lint the harness crate
+        working-directory: harness/opfs-contract
+        run: |
+          cargo fmt --all -- --check
+          cargo clippy --target wasm32-unknown-unknown --all-targets -- -D warnings
       - name: Install the harness
         working-directory: harness
         run: npm ci