add AGS767 fixtures and tests; consolidate vec README into shared fixture folder

Author: JaskRendix

tests/fixtures/ags717/README.md tests/fixtures/README.mdtests/fixtures/ags717/README.md renamed to tests/fixtures/README.md

@@ -0,0 +1,19 @@
+from pathlib import Path
+
+FIXTURE_DIR = Path(__file__).parent / "fixtures" / "ags767"
+
+
+def test_fixture_files_exist():
+    assert (FIXTURE_DIR / "078711.vec").exists()
+    assert (FIXTURE_DIR / "aircraft.air").exists()
+    assert (FIXTURE_DIR / "README.md").exists()
+
+
+def test_078711_vec_is_zip():
+    data = (FIXTURE_DIR / "078711.vec").read_bytes()
+    assert data.startswith(b"PK\x03\x04")  # ZIP magic
+
+
+def test_aircraft_air_is_utf16():
+    data = (FIXTURE_DIR / "aircraft.air").read_bytes()
+    assert data.startswith(b"\xff\xfe")  # UTF‑16LE BOM