[Fix] Session replies show visual-proof uploads as links

[roomote-roomote]

​Created by Roomote. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

Visual-proof uploads no longer trigger a separate parent Session event as soon as each image finishes uploading. The child task's explicit parent report remains responsible for sharing selected screenshot IDs through the existing native Slack image-block and Discord image payload paths. Other artifact types continue to notify the parent as before.

Why this change was made

The parent-report contract says visual-proof uploads are not shared automatically, but artifact upload completion still notified the parent for every artifact type. This let the parent create one link-based reply per screenshot before the child sent its consolidated report with image IDs.

Impact

Visual-proof screenshots stay private until the child report selects them, avoiding premature per-image link replies while preserving same-task/run authorization and native image delivery. The available Slack context exposes message text and file counts but not block payloads; Slack image blocks are not Slack file uploads, so fileCount alone cannot determine whether a recap displayed images.

[roomote-community]

No code issues found. See task

_{Reviewed e0c2edd}