Initial commit — Stage 0 project foundation

- Cargo workspace with engine, editor, tests crates
- oxide-editor binary stub (builds and runs cleanly)
- install.sh for Linux system installation
- README.md with logo, build and install instructions
- GPLv3 LICENSE
- .gitignore

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/Cargo.toml

@@ -0,0 +1,12 @@
+[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" }
+env_logger.workspace = true