Fix 1886 media cleanup policy (#1887)

* fix(media): track cleanup ownership per path

Add explicit cleanup policy handling to MediaStore and count refs by path before deleting the underlying file. This prevents cleanup from removing shared files until the final ref is gone.

Refs #1886

* fix(tools): keep send_file refs forget-only

Mark send_file media registrations as forget-only so cleanup drops the ref without deleting the original workspace file.

Refs #1886

* fix(channels): declare managed media cleanup policy

Explicitly mark downloaded and managed channel media as delete-on-cleanup so media ownership is visible at each registration site.

Refs #1886

pkg/channels/feishu/feishu_64.go

@@ -725,8 +725,9 @@ func (c *FeishuChannel) downloadResource(
 	out.Close()
 
 	ref, err := store.Store(localPath, media.MediaMeta{
-		Filename: filename,
-		Source:   "feishu",
+		Filename:      filename,
+		Source:        "feishu",
+		CleanupPolicy: media.CleanupPolicyDeleteOnCleanup,
 	}, scope)
 	if err != nil {
 		logger.ErrorCF("feishu", "Failed to store downloaded resource", map[string]any{