12.2: wordpress.org submission prep — screenshots, assets, readme polish

[tetakta]

Summary

• Real screenshots (settings/connect, domain verification, badge shortcode, badge widget) captured from a live WordPress instance (WordPress Playground) and added as screenshot-1..4.png
• readme.txt: expanded Screenshots section, added Upgrade Notice
• Fixed 2 real Plugin Check findings (unprefixed globals in settings-page.php)
• Icon/banner assets (128/256 icon, 772x250 banner) prepared separately for SVN assets, not included in this repo
• No changes to Premium/purchase flow (owner decision, stays "not for sale yet")

Test plan

• Verified live in WordPress Playground: settings page, domain verification state, badge shortcode render, badge widget in sidebar
• Local Plugin Check run (via Playground) — only real finding (unprefixed globals) fixed; remaining flags are text-domain-mismatch false positives caused by the GitHub archive folder name, not present when installed under the real tetapi slug (CI overrides slug explicitly)
• CI Plugin Check on this PR (authoritative, correct slug)

🤖 Generated with Claude Code

Co-Authored-By: Claude Fable 5 noreply@anthropic.com