Add codex app macOS launcher (#10418)

- Add `codex app <path>` to launch the Codex Desktop app.
- On macOS, auto-downloads the DMG if missing; non-macOS prints a link
to chatgpt.com/codex.

codex-rs/cli/Cargo.toml

@@ -40,6 +40,7 @@ owo-colors = { workspace = true }
 regex-lite = { workspace = true }
 serde_json = { workspace = true }
 supports-color = { workspace = true }
+tempfile = { workspace = true }
 tokio = { workspace = true, features = [
     "io-std",
     "macros",
@@ -59,4 +60,3 @@ assert_matches = { workspace = true }
 codex-utils-cargo-bin = { workspace = true }
 predicates = { workspace = true }
 pretty_assertions = { workspace = true }
-tempfile = { workspace = true }