Enable OpenTUI's Ghostty VT backed embedded terminal on FreeBSD.

OpenTUI only builds its Ghostty VT terminal core for linux/macos/windows and
otherwise falls back to a stub whose createEmbeddedTerminal() reports
"embedded terminal support is unavailable".  That stub makes the OpenCode TUI
crash as soon as it opens a terminal pane, so opt FreeBSD into the real
implementation (the vendored Ghostty already supports FreeBSD).

--- packages/native/build.zig.orig
+++ packages/native/build.zig
@@ -395,6 +395,7 @@
         .linux => target.result.abi.isMusl() or target.result.abi == .gnu,
         .macos => true,
         .windows => target.result.abi == .gnu,
+        .freebsd => true,
         else => false,
     };
 }