Docs: README and repo hygiene (2026-09-25 audit)

[pietechsolution]

Held for review. Please do not merge yet.

Changes

• RELEASE.md rewritten as a public release guide:
  • local machine paths removed (commands run from the repo root, with a VERSION variable)
  • the internal status/decision block and the settled slug-reversal section removed
  • kept: the automated release steps, the local checks, Plugin Check, the manual test pass, and the manual SVN recovery steps (ZIP build, trunk and tag, listing assets)
• README first paragraph now says what the plugin is (WordPress seating chart plugin), followed by a short company line.
• readme.txt is unchanged. The navincse contributor stays, as wordpress.org requires it.

Checks

• Docs only.