Keep backend test CI executable on Windows

The #295 unit suite now runs in CI, but the Windows clean runner exits before the lib test harness starts with STATUS_ENTRYPOINT_NOT_FOUND when optional native runtime entrypoints are absent. Windows still needs cfg/link coverage, while macOS and Linux can execute the shared Rust unit suite.

Constraint: Preserve the new Rust test gate without making optional Windows native runtime installation a CI prerequisite.
Rejected: Install Foundry/Windows App Runtime into every CI run | broader, slower, and unrelated to backend unit-test coverage.
Confidence: high
Scope-risk: narrow
Directive: Do not switch Windows back to executing the lib test binary until the optional native runtime dependency is present on the runner.
Tested: cargo test --manifest-path openless-all/app/src-tauri/Cargo.toml --lib
Not-tested: Windows CI rerun before push.

.github/workflows/ci.yml

@@ -92,8 +92,16 @@ jobs:
         run: cargo check --manifest-path src-tauri/Cargo.toml
 
       - name: Run Rust backend unit tests
+        if: runner.os != 'Windows'
         run: cargo test --manifest-path src-tauri/Cargo.toml --lib
 
+      - name: Compile Rust backend unit tests (Windows)
+        # Windows runner 能链接 lib test binary，但干净镜像缺少可选 native runtime
+        # DLL entrypoint 时，进程会在 test harness 启动前退出。这里保留 cfg/link
+        # 覆盖；共享单测在 macOS / Linux 上实际执行。
+        if: runner.os == 'Windows'
+        run: cargo test --manifest-path src-tauri/Cargo.toml --lib --no-run
+
       - name: Verify version sync across all 5 files
         # 两个平台都跑这个校验：Windows runner 自带 git-bash，跨 shell 表现一致。
         # 一旦版本号 drift 立刻 fail，避免发版时再发现漏改。