* fix: resolve runtime panic in Linux keychain integration
- Convert Linux keychain functions from sync (rt.block_on) to async
- Remove nested runtime panic when called from async context
- Make keychain API consistent across platforms (macOS, Linux, fallback)
- Propagate async through config loading and CLI commands
Fixes panic on Linux during 'ironclaw onboard' at Step 2 (Security).
* fix: await async Config::from_env in test_heartbeat example