tests(js_repl): remove node-related skip paths from js_repl tests (#12185)

## Summary
Remove js_repl/node test-skip paths and make Node setup explicit in CI
so js_repl tests always run instead of silently skipping.

## Why
We had multiple “expediency” skip paths that let js_repl tests pass
without actually exercising Node-backed behavior. This reduced CI signal
and hid runtime/environment regressions.

## What changed

### CI
- Added Node setup using `codex-rs/node-version.txt` in:
  - `.github/workflows/rust-ci.yml`
  - `.github/workflows/bazel.yml`
- Added a Unix PATH copy step in Bazel workflow to expose the setup-node
binary in common paths.

### js_repl test harness
- Added explicit js_repl sandbox test configuration helpers in:
  - `codex-rs/core/src/tools/js_repl/mod.rs`
  - `codex-rs/core/src/tools/handlers/js_repl.rs`
- Added Linux arg0 dispatch glue for js_repl tests so sandbox subprocess
entrypoint behavior is correct under Linux test execution.

### Removed skip behavior
- Deleted runtime guard function and early-return skips in js_repl tests
(`can_run_js_repl_runtime_tests` and related per-test short-circuits).
- Removed view_image integration test skip behavior:
  - dropped `skip_if_no_network!(Ok(()))`
- removed “skip on Node missing/too old” branch after js_repl output
inspection.

## Impact
- js_repl/node tests now consistently execute and fail loudly when the
environment is not correctly provisioned.
- CI has stronger signal for js_repl regressions instead of false green
from conditional skips.

## Testing
- `cargo test -p codex-core` (locally) to validate js_repl
unit/integration behavior with skips removed.
- CI expected to surface any remaining environment/runtime gaps directly
(rather than masking them).


#### [git stack](https://github.com/magus/git-stack-cli)
- ✅ `1` https://github.com/openai/codex/pull/12300
- ✅ `2` https://github.com/openai/codex/pull/12275
- ✅ `3` https://github.com/openai/codex/pull/12205
- ✅ `4` https://github.com/openai/codex/pull/12407
- ✅ `5` https://github.com/openai/codex/pull/12372
- 👉 `6` https://github.com/openai/codex/pull/12185
- ⏳ `7` https://github.com/openai/codex/pull/10673

codex-rs/core/src/tools/js_repl/mod.rs

@@ -1636,29 +1636,11 @@ mod tests {
     }
 
     async fn can_run_js_repl_runtime_tests() -> bool {
-        // These white-box runtime tests rely on the unit-test harness and are
-        // only required on macOS. Linux uses the codex-linux-sandbox arg0
-        // dispatch path, which is exercised in integration tests instead.
-        if !cfg!(target_os = "macos") {
-            return false;
-        }
-        if std::env::var_os("CODEX_SANDBOX").is_some() {
-            return false;
-        }
-        let Some(node_path) = resolve_node(None) else {
-            return false;
-        };
-        let required = match required_node_version() {
-            Ok(v) => v,
-            Err(_) => return false,
-        };
-        let found = match read_node_version(&node_path).await {
-            Ok(v) => v,
-            Err(_) => return false,
-        };
-        found >= required
+        // These white-box runtime tests are required on macOS. Linux relies on
+        // the codex-linux-sandbox arg0 dispatch path, which is exercised in
+        // integration tests instead.
+        cfg!(target_os = "macos")
     }
-
     fn write_js_repl_test_package(base: &Path, name: &str, value: &str) -> anyhow::Result<()> {
         let pkg_dir = base.join("node_modules").join(name);
         fs::create_dir_all(&pkg_dir)?;