Add scope abacus pixel art

[KLSGG]

Summary

• Add original 128x128 PNG pixel art at assets/pixel-art/scope-abacus.png.
• Add a deterministic standard-library generator at assets/pixel-art/generate_scope_abacus.py so reviewers can reproduce the asset.
• Add a short demo video at demos/scope-abacus-demo.ogv.

/claim #80

Creative note: I made a scope abacus with colored proof beads for evidence, review, merge, and payout on a compact circuit desk, because it fits the bounty workflow while staying distinct from recent dry dock, orbit station, altar, elevator, greenhouse, train, switchboard, kiln, and loom submissions.

Validation

• python3 assets/pixel-art/generate_scope_abacus.py
• python3 -m py_compile assets/pixel-art/generate_scope_abacus.py
• file assets/pixel-art/scope-abacus.png -> 128 x 128 RGBA PNG
• PNG header parsed locally as 128x128
• Reproduced PNG SHA-256: 97805deb58c6e529c342a5e27dd42583778b8f4404cc9abfb241e1a7144c42b5
• file demos/scope-abacus-demo.ogv -> Ogg data, Theora video
• ffprobe confirmed Theora video, 720x720, 6 seconds
• git diff --check --cached before commit