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.

agent/tests/util.go

@@ -0,0 +1,21 @@
+package tests
+
+import (
+	"fmt"
+	"os"
+)
+
+// readFile is used by stages that need to peek at /sys files without
+// importing the agent's probes package (which would cycle).
+func readFile(p string) ([]byte, error) {
+	return os.ReadFile(p)
+}
+
+// formatCount pluralizes a count + label: (0, "disk") → "0 disks",
+// (1, "disk") → "1 disk", (n, "disk") → "n disks". Keeps log lines tidy.
+func formatCount(n int, label string) string {
+	if n == 1 {
+		return fmt.Sprintf("%d %s", n, label)
+	}
+	return fmt.Sprintf("%d %ss", n, label)
+}