Parser now tags ``mutator`` / ``decky_mutated`` lines with ``kind="mutation"``
so the engine can route them into a sibling ``_mutations`` index keyed
by decky name instead of the per-IP attacker index. ``traversals()``
joins the two streams: every attacker gets a ``mutations_during`` list
of markers from touched deckies bounded by their first/last-seen
window. ``AttackerTraversal.to_dict()`` grows a ``mutations_during``
field and a ``timeline`` that chronologically interleaves hops and
markers, so an ``SSH at T5 → mutation at T6 → HTTP at T7`` substrate
transition is visible to UI consumers instead of reading as a silent
discontinuity.
The existing hops-only JSON shape is preserved; old clients that
ignore unknown keys keep working.
