Offer T3 Code as the preferred agent, opening a thread in the Panama project, and install it with the desktop

setup/packages/desktop-packages

@@ -86,6 +86,10 @@ rbw
 # The Snapshots page is snapper end to end; see scripts/panama-snapshots.
 snapper
 sushi
+# T3 Code, from Terra: the desktop app, its background server and the `t3` CLI.
+# panama-agent opens a T3 thread when preferredAgent is t3, and the ticket
+# skill renders its plans and mocks into T3 threads.
+t3code
 # Fonts the desktop names by family and would otherwise render as tofu.
 # VictorMono is required: it draws every glyph in the shell.
 victormono-nerd-fonts