Merges xmrcheckout/xmrcheckout main (7 commits since 655d037):
- Add Monero system status and reconciler heartbeat
- Surface Monero health status in UI (dashboard + invoice pages)
- Harden reconciler status heartbeat startup
- Avoid false Monero outage states in UI
- Cache Monero connectivity in system status
- Next.js security patch (15.5.9 → 15.5.14)
- Bump Monero Docker defaults to 0.18.4.6
Resolved conflicts in reconciler.py (kept our advisory lock + upstream
heartbeat), routes.py (kept both imports), README.md (kept both sections).
jwinterm