v0.5.2 — worktrees for every thread type

Some threads (forks/continues) never receive a SessionStart event from the engine, so they got no auto worktree. The hook now also listens to UserPromptSubmit: every prompt re-checks (idempotently, ~50ms, silent when the session is already bound) and schedules the worktree on the first message if needed. 130 tests green.