docs: drop EOL release table, align node floor with engines

Remove the release/EOL table from the README — the dates were stale and
EOL policy is better tracked via release notes. Bump the documented
Node.js floor from >= 22.12 to >= 22.12.0 to match engines.node exactly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>