fix: address PR review feedback across channel system

- MediaStore: use full UUID to prevent ref collisions, preserve and
  expose metadata via ResolveWithMeta, include underlying OS errors
- Agent loop: populate MediaPart Type/Filename/ContentType from
  MediaStore metadata so channels can dispatch media correctly
- SplitMessage: fix byte-vs-rune index mixup in code block header
  parsing, remove dead candidateStr variable
- Pico auth: restrict query-param token behind AllowTokenQuery config
  flag (default false) to prevent token leakage via logs/referer
- HandleMessage: replace context.TODO with caller-propagated ctx,
  log PublishInbound failures instead of silently discarding
- Gateway shutdown: use fresh 15s timeout context for StopAll so
  graceful shutdown is not short-circuited by the cancelled parent ctx

pkg/channels/feishu/feishu_64.go

@@ -131,7 +131,7 @@ func (c *FeishuChannel) Send(ctx context.Context, msg bus.OutboundMessage) error
 	return nil
 }
 
-func (c *FeishuChannel) handleMessageReceive(_ context.Context, event *larkim.P2MessageReceiveV1) error {
+func (c *FeishuChannel) handleMessageReceive(ctx context.Context, event *larkim.P2MessageReceiveV1) error {
 	if event == nil || event.Event == nil || event.Event.Message == nil {
 		return nil
 	}
@@ -189,7 +189,7 @@ func (c *FeishuChannel) handleMessageReceive(_ context.Context, event *larkim.P2
 		"preview":   utils.Truncate(content, 80),
 	})
 
-	c.HandleMessage(peer, messageID, senderID, chatID, content, nil, metadata)
+	c.HandleMessage(ctx, peer, messageID, senderID, chatID, content, nil, metadata)
 	return nil
 }