feat: enhance Safew watcher initialization and token management

- Added functionality to list and start Safew tokens in the main server function, ensuring proper initialization of the Safew watcher.
- Introduced `ensureSafewWatcher` method in the ChannelHandler to manage Safew tokens during channel creation and updates.
- Implemented `StartTokens` method in the Watcher to handle multiple tokens efficiently.
- Enhanced error handling and logging for Safew watcher operations to improve observability.

cmd/server/main.go

@@ -139,6 +139,12 @@ func main() {
 	}
 	safewWatcher := safew.NewWatcher(watcherStore, poller)
 	defer safewWatcher.Stop()
+	if tokens, err := st.ListSafewTokens(context.Background()); err != nil {
+		slog.Warn("list safew tokens", "error", err)
+	} else {
+		safewWatcher.StartTokens(tokens)
+		slog.Info("safew watchers ensured", "count", len(tokens))
+	}
 
 	channelH := handler.NewChannelHandler(st, redisCache, safewWatcher)
 	ruleH := handler.NewRuleHandler(st, redisCache)