feat(webui): add Install to Disk page

Expose the existing bee-install script through the web UI:
- platform/install.go: remove USB exclusion, add SizeBytes/MountedParts
  fields, add MinInstallBytes()/DiskWarnings() safety checks (size,
  mounted partitions, toram+low-RAM warning)
- webui: add GET /api/install/disks, POST /api/install/run,
  GET /api/install/stream endpoints
- webui: add Install to Disk page with disk table, warning badges,
  device-name confirmation gate, SSE progress terminal, reboot button

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

audit/internal/webui/server.go

@@ -84,6 +84,9 @@ type handler struct {
 	// per-GPU rings (index = GPU index)
 	gpuRings    []*gpuRings
 	ringsMu     sync.Mutex
+	// install job (at most one at a time)
+	installJob  *jobState
+	installMu   sync.Mutex
 }
 
 // NewHandler creates the HTTP mux with all routes.
@@ -149,6 +152,11 @@ func NewHandler(opts HandlerOptions) http.Handler {
 	// Preflight
 	mux.HandleFunc("GET /api/preflight", h.handleAPIPreflight)
 
+	// Install
+	mux.HandleFunc("GET /api/install/disks", h.handleAPIInstallDisks)
+	mux.HandleFunc("POST /api/install/run", h.handleAPIInstallRun)
+	mux.HandleFunc("GET /api/install/stream", h.handleAPIInstallStream)
+
 	// Metrics — SSE stream of live sensor data + server-side SVG charts
 	mux.HandleFunc("GET /api/metrics/stream", h.handleAPIMetricsStream)
 	mux.HandleFunc("GET /api/metrics/chart/", h.handleMetricsChartSVG)