feat: container orchestration, branding overhaul, onboarding logging

Container orchestration:
- Health monitor with crash recovery and auto-restart
- Doctor service (periodic health checks via systemd timer)
- Reconcile service (desired-state convergence)
- Stack-aware install/uninstall with dependency tracking

Branding:
- Custom GRUB background (designer artwork, 1024x768)
- ISOLINUX boot menu: centered, orange accents, clean labels
- Terminal banners: adaptive width, basic ANSI colors, fits 80-col
- Removed auto-generated splash scripts (designer provides assets)
- GRUB theme: lowercase branding

Frontend:
- 401 handler clears localStorage immediately (prevents cascade)

Backend:
- Onboarding/auth logging ([onboarding] tag in journalctl)
- Cookie Secure flag logging for debugging HTTP/HTTPS issues

ISO fixes:
- Install log saved before unmount (was silently failing)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

image-recipe/configs/archipelago.service

@@ -16,6 +16,8 @@ Restart=on-failure
 RestartSec=5
 WatchdogSec=300
 TimeoutStartSec=300
+# Bitcoin Core needs up to 600s to flush UTXO set on shutdown
+TimeoutStopSec=660
 
 # Filesystem protection
 ProtectSystem=strict