release: bundle bwrap with Linux codex DotSlash artifact (#21312)

## Why

#21255 changed the Linux sandbox fallback so Codex can use a bundled
`codex-resources/bwrap` executable when no suitable system `bwrap` is
available. That lookup is relative to the native Codex executable
returned by
`std::env::current_exe()`, as implemented in
[`bundled_bwrap.rs`](9766d3d51c/codex-rs/linux-sandbox/src/bundled_bwrap.rs (L83-L93)).

The release already publishes a separate `bwrap` DotSlash output, but
the Linux `codex` DotSlash output still pointed at a single-binary
`.zst` payload. Running the `codex` DotSlash manifest only materializes
the native `codex` executable; it does not also create sibling files
from the separate `bwrap` manifest. The fallback path therefore needs
the Linux `codex` DotSlash artifact itself to include the real `bwrap`
executable at `codex-resources/bwrap`.

## What changed

- stage a Linux primary `codex-<target>-bundle.tar.zst` release artifact
containing `codex` and `codex-resources/bwrap`
- point the Linux `codex` DotSlash outputs at that bundle tarball
- leave the standalone `bwrap` DotSlash output in place for consumers
that want to fetch `bwrap` directly

## Verification

- `jq . .github/dotslash-config.json`
- Ruby YAML parse of `.github/workflows/rust-release.yml`

.github/dotslash-config.json

@@ -11,11 +11,11 @@
           "path": "codex"
         },
         "linux-x86_64": {
-          "regex": "^codex-x86_64-unknown-linux-musl\\.zst$",
+          "regex": "^codex-x86_64-unknown-linux-musl-bundle\\.tar\\.zst$",
           "path": "codex"
         },
         "linux-aarch64": {
-          "regex": "^codex-aarch64-unknown-linux-musl\\.zst$",
+          "regex": "^codex-aarch64-unknown-linux-musl-bundle\\.tar\\.zst$",
           "path": "codex"
         },
         "windows-x86_64": {