docs: fix broken repository images

[auroraxo]

Summary

• restore the README logo from a byte-identical SVG already present in the repository history
• remove four dead, nonessential GitHub attachment embeds while preserving their surrounding roadmap prose
• eliminate all five broken image references reported in Five documentation images, including README hero, return 404 #16288

Verification

• confirmed each original github.com/user-attachments/assets/... URL returns HTTP 404
• verified the restored SVG matches the historical repository blob by SHA-256
• checked that no reported dead attachment URL remains in the three affected Markdown files
• ran git diff --check

Closes #16288

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