[svadrutk]

Summary

• Replace the four relative Slack screenshot paths with absolute raw.githubusercontent.com URLs.
• The live website resolves relative assets to a missing site path (404); the source PNG URLs return 200.
• Follow-up fix for docs: add Slack setup screenshots and describe the scope picker #223; leaves the assets and metadata unchanged.

Validation

• Slack guide lint passes.
• All four screenshot URLs return HTTP 200 with image/png content.
• git diff --check passes.