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>

CHANGELOG.md

@@ -38,6 +38,12 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Removed
 
+- **Dead-code sweep.** The legacy free-function git API (with its latent
+  pipe deadlock), ToolCheck, the fd-passing-era libc bindings, the GraphView
+  placeholder, the superseded ColumnHat widget, the tmux-era
+  TranscriptPublisher, the committed `ptyc` binary, and the unused
+  `mocktail` dev-dependency (D-25 amended) are gone. (T-385)
+
 - **Dead welcome-screen tiles.** "Clone from git…" and "Start a Claude
   session" did nothing on tap and advertised shortcuts that were never
   registered; the tips card now lists only shortcuts that exist in the