build(linux): carry the pinned Node inside the AppImage so serve's slot works offline (#28204)

* build(linux): carry the pinned Node inside the AppImage so orca serve's slot works offline

Linux packaging places the pinned glibc Node at resources/node-runtime/bin/node before the
glibc-floor gate, proves it serves one PTY with the packaged daemon entry, and deb/rpm exclude
it through fpm. orca serve's orcad slot copies that Node (hash-checked) instead of downloading.

* test(serve): type the bundled Node fixture

---------

Co-authored-by: m4air <m4air@Mac.localdomain>

src/shared/appimage-node-runtime.ts

@@ -0,0 +1,24 @@
+/**
+ * The pinned Node a Linux AppImage carries, so what runs outside Electron needs no download.
+ * deb and rpm exclude it at packaging time: their installs never vanish under a running process.
+ *
+ * Keep this file erasable-only TypeScript with no imports — packaging scripts require it directly.
+ */
+
+/** Segments under the app's resources dir, laid out like the upstream archive (`bin/node`). */
+export const APPIMAGE_NODE_RUNTIME_SEGMENTS = ['node-runtime', 'bin', 'node'] as const
+/** fpm `--exclude` pattern, matched against each staged path (`*` crosses `/` there). */
+export const APPIMAGE_NODE_RUNTIME_FPM_EXCLUDE = '*/resources/node-runtime'
+
+/** AppImages are glibc builds, so only a glibc host of the same CPU can use the bundled Node. */
+export function appImageNodeRuntimeTarget(
+  arch: string
+): 'linux-x64-glibc' | 'linux-arm64-glibc' | null {
+  if (arch === 'x64') {
+    return 'linux-x64-glibc'
+  }
+  if (arch === 'arm64') {
+    return 'linux-arm64-glibc'
+  }
+  return null
+}