add a codex app environment

.codex/environments/environment.toml

@@ -0,0 +1,23 @@
+# THIS IS AUTOGENERATED. DO NOT EDIT MANUALLY
+version = 1
+name = "codex-cli"
+
+[setup]
+script = '''
+cd codex-rs
+
+rustup component add rustfmt
+rustup component add clippy
+# Install helper tools used by the workspace justfile:
+cargo install just
+# Optional: install nextest for the `just test` helper
+cargo install cargo-nextest
+
+# Build Codex.
+cargo build
+'''
+
+[[actions]]
+name = ""
+icon = "tool"
+command = ""