[codex] Prepare plugin for WordPress.org submission

[dhanson-wp]

Summary

• Move compiled block assets from build/ to compiled/ so PressShip includes runtime files in submission ZIPs.
• Add PressShip/repo hygiene files and tighten README/readme copy for WordPress.org review.
• Harden the block markup and frontend behavior with a real button, normalized attribute-derived values, reduced-motion-aware scrolling, and safer hide-after-scroll focus handling.

Validation

• npm run lint:js
• npm run lint:css
• npm run build
• php -l scroll-indicator.php
• npm audit --omit=dev --audit-level=high
• npx pressship publish . --dry-run
• WordPress Playground smoke on --wp=7.0 / PHP 8.3, currently resolving to WordPress 7.0-RC5: activate, insert block, publish, frontend click/keyboard, editor reload validation.

Notes

• Tested up to remains 6.9 until Playground resolves --wp=7.0 to final stable 7.0 rather than RC5.

[dhanson-wp]

Manual test Playground for this branch:

https://playground.wordpress.net/#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

Note: hosted Playground currently 404s for exact wp: 7.0, so this uses wp: nightly. Local Playground CLI still resolves --wp=7.0 to 7.0-RC5 and passed the smoke test.

[dhanson-wp]

Corrected manual test Playground for this branch:

https://playground.wordpress.net/#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

Verified: this boots, opens the editor, and the Scroll Indicator block appears in the inserter search.