drop the unused mocktail dep; amend D-25 (T-385)

mocktail was pinned and documented as the IO-mocking strategy, but
after the T-91 coverage drive it had zero imports — every IO seam
ended up with an injected hand-rolled fake instead. D-25 is amended
to record that the hand-rolled-fakes rule covers IO seams too;
licenses.yaml and the lockfile follow. The ptyc binary removal noted
in this sweep landed with the git-API commit (it was already staged).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pubspec.yaml

@@ -69,7 +69,6 @@ dev_dependencies:
   # Held at 1.31.0: flutter_test SDK-locks the resolvable ceiling here
   # (1.31.1 is latest but not reachable under our Flutter pin).
   test: 1.31.0
-  mocktail: 1.0.5
   # Held at 0.12.1: 0.13.0 disabled anti-aliasing on text painting, which
   # churns every golden. Dev-only, no advisory — defer the golden re-baseline
   # to its own change (T-353).