Initial commit: full Phases 1-6 implementation

Post-repair hardware validation pipeline for Proxmox cluster hosts.
Go orchestrator + in-image agent + mkosi live image + bundled dnsmasq
PXE + SQLite + HTMX/SSE UI + notify registry + janitor + full docs.

live-image/mkosi.skeleton/etc/systemd/system/vetting-agent.service

@@ -0,0 +1,18 @@
+[Unit]
+Description=Vetting hardware-validation agent
+# Wait until networking is minimally up (the agent itself retries
+# dial failures, but no point hammering before DHCP finishes).
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+ExecStart=/usr/local/sbin/vetting-agent
+Restart=on-failure
+RestartSec=5s
+# The agent reads /proc/cmdline; it needs no extra env.
+StandardOutput=journal+console
+StandardError=journal+console
+
+[Install]
+WantedBy=multi-user.target