refactor(repo): promote tauri app to repository root

src-tauri/tests/README.md

@@ -0,0 +1,27 @@
+# Headless Download Engine Tests
+
+Run the full Rust suite:
+
+```sh
+cd src-tauri
+cargo test --all-targets
+```
+
+Run only the async download integration harness with deterministic serial
+performance measurements and visible test output:
+
+```sh
+cd src-tauri
+RUST_BACKTRACE=1 cargo test --test download_engine -- --test-threads=1 --nocapture
+```
+
+The harness binds an ephemeral loopback port and requires no GUI, external
+network access, or bundled media binaries. It validates:
+
+- aggregation of many streamed HTTP body chunks;
+- pause and ranged resume through `DownloadCoordinator`;
+- cancellation and partial-file cleanup;
+- SHA-256 integrity after resume;
+- retry recovery from transient HTTP failures;
+- terminal error reporting after the retry budget is exhausted;
+- a five-second local transfer performance budget for a 3 MiB fixture.