Initial implementation: host lifecycle + PXE + admin dashboard

Go service for Proxmox homelab cluster provisioning. Handles PXE boot,
Proxmox autoinstall (answer file generation), cluster join via SSH,
and Infrastructure API registration.

- Host state machine (registered → pxe_ready → installing → ready)
- dnsmasq supervisor with MAC-based allowlist
- iPXE script and Proxmox answer file generation
- First-boot phone-home → cluster join → infra registration
- Operation locking with expiry (409 on conflict)
- SSE event hub for real-time dashboard updates
- Admin dashboard (host grid, detail, registration form)
- Config-driven server types with hot-reload
- Docker deployment (multi-stage fat image)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/pxe/ipxe.go

@@ -0,0 +1,19 @@
+package pxe
+
+import (
+	"fmt"
+
+	"provisioning/internal/model"
+)
+
+func BuildIPXEScript(publicURL string, img *model.Image, mac string) string {
+	kernelURL := fmt.Sprintf("%s/images/boot/%s/%s", publicURL, img.Name, "linux26")
+	initrdURL := fmt.Sprintf("%s/images/boot/%s/%s", publicURL, img.Name, "initrd.img")
+
+	return fmt.Sprintf(`#!ipxe
+echo Provisioning: booting %s on ${mac}
+kernel %s vga=791 video=vesafb:lfb:on
+initrd %s
+boot
+`, img.Name, kernelURL, initrdURL)
+}