feat(webui): sync host clock and timezone from browser

Adds POST /api/system/time-sync so the dashboard's "Sync with this
browser" button can set the host's date, time, and IANA timezone from
the client's browser — useful for appliances with no NTP/network
access to keep their own clock straight. Disables NTP before writing
the manual time so it doesn't get immediately overwritten.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

audit/internal/webui/server.go

@@ -346,6 +346,7 @@ func NewHandler(opts HandlerOptions) http.Handler {
 	mux.HandleFunc("POST /api/system/install-to-ram", h.handleAPIInstallToRAM)
 	mux.HandleFunc("POST /api/system/reboot", h.handleAPISystemReboot)
 	mux.HandleFunc("POST /api/system/shutdown", h.handleAPISystemShutdown)
+	mux.HandleFunc("POST /api/system/time-sync", h.handleAPISystemTimeSync)
 
 	// Preflight
 	mux.HandleFunc("GET /api/preflight", h.handleAPIPreflight)