chore: move tweet draft out of public wiki

wiki/research-lab/posts/alpha-191-in-2026.tweet.md was an internal
marketing draft (pre-flight checklist + draft tweet text) that should
not have been committed to a public path. Moved to docs/alpha-zoo/
(gitignored) and removed from main.

Note: the file remains in git history at commit 7912b77. If history
scrub is required, a force-push rewrite is needed (separate decision).

Author: warren618