Document parity plan and add engine unit tests

Data/Engine/tests/test_sqlite_migrations.py

@@ -0,0 +1,32 @@
+import sqlite3
+import unittest
+
+from Data.Engine.repositories.sqlite import migrations
+
+
+class MigrationTests(unittest.TestCase):
+    def test_apply_all_creates_expected_tables(self) -> None:
+        conn = sqlite3.connect(":memory:")
+        try:
+            migrations.apply_all(conn)
+            cursor = conn.cursor()
+            tables = {
+                row[0]
+                for row in cursor.execute(
+                    "SELECT name FROM sqlite_master WHERE type='table'"
+                )
+            }
+
+            self.assertIn("devices", tables)
+            self.assertIn("refresh_tokens", tables)
+            self.assertIn("enrollment_install_codes", tables)
+            self.assertIn("device_approvals", tables)
+            self.assertIn("scheduled_jobs", tables)
+            self.assertIn("scheduled_job_runs", tables)
+            self.assertIn("github_token", tables)
+        finally:
+            conn.close()
+
+
+if __name__ == "__main__":  # pragma: no cover - convenience for local runs
+    unittest.main()