fix: Ensure offset fetch checks SMQ storage as fallback

This minimal fix addresses offset persistence issues during consumer
group operations without introducing timeouts or delays.

KEY CHANGES:
1. OffsetFetch now checks SMQ storage as fallback when offset not found in memory
2. Immediately cache offsets in in-memory map after SMQ fetch
3. Prevents future SMQ lookups for same offset
4. No retry logic or delays that could cause timeouts

ROOT CAUSE:
When offsets are persisted to SMQ but not yet in memory cache,
consumers would get -1 (not found) and default to offset 0 or
auto.offset.reset, causing message loss.

FIX:
Simple fallback to SMQ + immediate cache ensures offset is always
available for subsequent queries without delays.

weed/mq/kafka/protocol/offset_management.go

@@ -268,6 +268,8 @@ func (h *Handler) handleOffsetFetch(correlationID uint32, apiVersion uint16, req
 				if off, meta, err := h.fetchOffsetFromSMQ(key); err == nil && off >= 0 {
 					fetchedOffset = off
 					metadata = meta
+					// Load into in-memory cache for future queries
+					_ = h.commitOffset(group, topic.Name, partition, off, meta)
 					glog.V(4).Infof("[OFFSET_FETCH] Found in storage: group=%s topic=%s partition=%d offset=%d",
 						request.GroupID, topic.Name, partition, off)
 				} else {