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>

deploy/server-types.example.yaml

@@ -0,0 +1,22 @@
+server_types:
+  minisforum-ms-01:
+    display_name: "Minisforum MS-01"
+    boot_disk: "/dev/nvme0n1"
+    management_nic: "enp2s0"
+    gpu: false
+    hostname_prefix: "pve-ms"
+    expected_nics:
+      - name: "enp2s0"
+        speed: "2500"
+      - name: "enp3s0"
+        speed: "2500"
+
+  minisforum-um790:
+    display_name: "Minisforum UM790 Pro"
+    boot_disk: "/dev/nvme0n1"
+    management_nic: "enp1s0"
+    gpu: true
+    hostname_prefix: "pve-um"
+    expected_nics:
+      - name: "enp1s0"
+        speed: "2500"