Import Oxide engine (Stages 0–10) under MIT license

Full project snapshot migrated to new Gitea remote without history:
engine, editor, physics, script, examples, tests, docs, and assets.
Relicensed from GPLv3 to MIT and updated repo URLs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "oxide-tests"
+description = "Oxide Engine — integration test harness"
+version.workspace = true
+edition.workspace = true
+authors.workspace = true
+license.workspace = true
+rust-version.workspace = true
+
+[dev-dependencies]
+oxide-engine = { path = "../engine" }
+oxide-editor = { path = "../editor" }
+env_logger.workspace = true
+serde.workspace = true