Add BDD scenarios that capture bug #4739 — the missing TUI SQLite
session persistence layer. The cleveragents.tui.session_store module
and TuiSessionStore class do not exist; these tests verify their
absence and will pass once the implementation is in place.
All scenarios are tagged @tdd_expected_fail so CI passes while the
module is absent. The expected-fail mechanism inverts the result:
a failing AssertionError means the bug still exists (CI passes).
ISSUES CLOSED: #10879