add a Makefile for the common commands, and a test reporter

The invocations in CLAUDE.md were correct but long, and retyping them is how
flags get dropped. `make check` is the gate a change should pass: Yarn compiles,
voice sheets are in sync, EditMode is green.

`make test` and `make build` depend on a `lock` target that fails if the Editor
has the project open, which removes the most common confusing failure. It
filters out AssetImportWorker children, which are not a second Editor.

tools/ci/report_tests.py parses the NUnit results and exits non-zero on failure,
because Unity documents no common exit-code definition across the components
under test — the XML is the authority, not $?.

`make merge-driver` configures UnityYAMLMerge for the .gitattributes rules added
earlier. Note the binary lives in the Editor bundle under Contents/Helpers, not
Contents/Tools as most guides say; there is no Tools directory in Unity 6 on
macOS.

Also ignores the local .test-results/ and build/ output.

Co-Authored-By: Claude Opus 5 <[email protected]>

.gitignore

@@ -127,3 +127,9 @@ tools/**/obj/
 *.tar.gz
 *.7z
 *.rar
+
+# ---------------------------------------------------------------------------
+# Local build and test output (Makefile targets)
+# ---------------------------------------------------------------------------
+/.test-results/
+/build/