feat(collect): remove power-on/off, add skip-hung for Redfish collection

Remove power-on and power-off functionality from the Redfish collector;
keep host power-state detection and show a warning in the UI when the
host is powered off before collection starts.

Add a "Пропустить зависшие" (skip hung) button that lets the user abort
stuck Redfish collection phases without losing already-collected data.
Introduces a two-level context model in Collect(): the outer job context
covers the full lifecycle including replay; an inner collectCtx covers
snapshot, prefetch, and plan-B phases only. Closing the skipCh cancels
collectCtx immediately — aborts all in-flight HTTP requests and exits
plan-B loops — then replay runs on whatever rawTree was collected.

Signal path: UI → POST /api/collect/{id}/skip → JobManager.SkipJob()
→ close(skipCh) → goroutine in Collect() → cancelCollect().

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

internal/server/server.go

@@ -99,6 +99,7 @@ func (s *Server) setupRoutes() {
 	s.mux.HandleFunc("POST /api/collect/probe", s.handleCollectProbe)
 	s.mux.HandleFunc("GET /api/collect/{id}", s.handleCollectStatus)
 	s.mux.HandleFunc("POST /api/collect/{id}/cancel", s.handleCollectCancel)
+	s.mux.HandleFunc("POST /api/collect/{id}/skip", s.handleCollectSkip)
 }
 
 func (s *Server) Run() error {