docs: rewrite wp.org plugin page, leaner copy, video embed, screenshots

[AllTerrainDeveloper]

What

Rewrites the WordPress.org plugin page (readme.txt) to be more compelling: fewer words, more demonstrative visuals, better directory SEO.

Changes

readme.txt

• Description cut from a 12-bullet feature dump to four short benefit-led sections: A real desktop, Make it yours, Superpowers, Built to be extended.
• YouTube teaser (https://www.youtube.com/watch?v=jii_gGbqUx4) embedded at the top of the description. wp.org auto-embeds YouTube URLs on their own line; direct video uploads to the SVN assets dir are not supported, so the link is the only option.
• Short description and tags tuned for plugin-directory search (ui → dashboard).
• "AI Copilot" renamed to "AI Assistant" throughout the page body to match the UI (changelog entries left as-is).
• External services disclosure, Installation, FAQ, and Changelog otherwise untouched.

Screenshots — seven added to .wordpress-org/, deployed to the SVN assets dir by the 10up action on the next release tag:

1. Multitasking hero — four admin windows side by side
2. Custom wallpaper + plugin widgets
3. AI Assistant (Cmd+K)
4. Content Graph
5. OS Settings wallpaper picker
6. Files on the desktop
7. Recycle Bin

Notes

• Content-only change; npm run build ran clean with no asset diffs.
• The new page goes live on wp.org with the next release (or a manual SVN commit if wanted sooner).

[AllTerrainDeveloper]