fix: correct daily work/break calculations and league back button

- ComputeDailyTotals: only assume working from dayStart when first event
  is 'out' (cross-midnight session); otherwise start idle. Fixes inflated
  work/break counts in reports, status, export, burnout, salary, and RPG.
- leagueToggleCallback: add settings back keyboard when RPG is disabled.
- webhook: add graceful HTTP server shutdown on context cancellation.

internal/handler/settings.go

@@ -144,7 +144,8 @@ func (h *Handler) leagueToggleCallback(ctx context.Context, chatID int64, msgID
 		return
 	}
 	if !st.RPGEnabled {
-		h.editText(ctx, chatID, msgID, "League requires the RPG system. Enable RPG first in Settings.", nil)
+		kb := settingsBackKeyboard()
+		h.editText(ctx, chatID, msgID, "League requires the RPG system. Enable RPG first in Settings.", &kb)
 		return
 	}
 	text, kb := h.buildToggleKeyboard(user.ID, "league", "WorkTime League")