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.postinst

@@ -0,0 +1,15 @@
+#!/bin/sh
+# mkosi postinst: install the vetting-agent binary and its systemd unit
+# into the image. The binary must already be built for linux-amd64 at
+# repo root under bin/vetting-agent.linux-amd64 (the top-level Makefile
+# does this via `make agent-linux`).
+set -eu
+
+AGENT_BIN="${SRCDIR:-..}/bin/vetting-agent.linux-amd64"
+
+install -D -m 0755 "$AGENT_BIN" "$BUILDROOT/usr/local/sbin/vetting-agent"
+install -D -m 0644 "$SRCDIR/mkosi.skeleton/etc/systemd/system/vetting-agent.service" \
+    "$BUILDROOT/etc/systemd/system/vetting-agent.service"
+
+ln -sf /etc/systemd/system/vetting-agent.service \
+    "$BUILDROOT/etc/systemd/system/multi-user.target.wants/vetting-agent.service"