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/web/static/app.js

@@ -0,0 +1,23 @@
+(function() {
+  const dot = document.getElementById('sse-dot');
+  let es;
+
+  function connect() {
+    es = new EventSource('/events');
+    es.addEventListener('hello', () => {
+      dot.classList.remove('disconnected');
+    });
+    es.addEventListener('host.state_changed', (e) => {
+      // Reload the page to reflect state changes
+      // Future: HTMX swap individual tiles
+      window.location.reload();
+    });
+    es.onerror = () => {
+      dot.classList.add('disconnected');
+      es.close();
+      setTimeout(connect, 3000);
+    };
+  }
+
+  connect();
+})();