Delete docs/plans/SESSION-STATE.md

The pre-publish handoff note is retired: main b26bb55 passed every pre-tag gate for 3.4.4 and the remaining steps (#50, the tag push) are Elliot's. Planning notes under docs/plans/ are not logged in CHANGELOG.md, so no entry or version bump.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: ElliotDrel