fix: resolve 8 architecture flaws across download, playlist, and webhook

- Add --continue and --max-filesize to yt-dlp for download resilience
- Route thumbnail downloads through HTTP_PROXY
- Show per-video progress (i/N) with cancel for playlist downloads
- Run playlist asynchronously so cancel callbacks can be processed
- Guard handlePlaylistConfirm against concurrent active jobs
- Close Done channel in playlist entry lifecycle
- Add stepState TTL (30 min) to prevent stale states
- Wrap webhook server for graceful shutdown on SIGTERM
- Refactor formatBytes to loop-based implementation
- Show first line of stderr in user-facing error messages
- Fix format pointer reuse in playlist loop
- Add CreatedAt field to stepState for TTL tracking
- Add MaxFileSize and ProgressPrefix fields to DownloadJob

internal/handler/search.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/go-telegram/bot/models"
 
@@ -39,7 +40,7 @@ func (h *Handler) handleSearchQuery(ctx context.Context, chatID int64, text stri
 		PerPage: 5,
 		Source:  source,
 	}
-	ss := &stepState{SearchState: state}
+	ss := &stepState{SearchState: state, CreatedAt: time.Now()}
 	h.setUserStepState(chatID, ss)
 
 	kb := searchResultsKeyboard(state)