feat: ARM tarball builds + arch-aware download (#2248)

* feat: ARM tarball builds + arch-aware download

- Add ARM64 matrix entries for native binary agents (zeroclaw, opencode,
  hermes, claude) in agent-tarballs.yml workflow
- Update agent-tarball.ts to detect remote VM arch via uname -m and
  download the correct tarball (x86_64 or arm64)
- Change release strategy to support multiple arch assets per tag
- Document ARM build requirements in discovery.md for future agents
- Bump CLI version to 0.15.2

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: use sudo for tarball extraction on non-root SSH clouds

On AWS Lightsail, SSH connects as 'ubuntu' (not root), but tarballs
extract to /root/. Without sudo, tar fails with "Permission denied".
Conditionally use sudo when not running as root (id -u != 0).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

packages/cli/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@openrouter/spawn",
-  "version": "0.15.1",
+  "version": "0.15.2",
   "type": "module",
   "bin": {
     "spawn": "cli.js"