E6: remove build-tool plugin (architecturally incompatible with the
monorepo-only CLI); rewrite the command plugin as a thin pass-through to
swift-gtk-gen.
E7: add swift-format as a dependency, format generated output in-process
before writeIfChanged, re-enable swift format lint --strict in
compile-gate.sh. CamelCase renderer identifiers (enum/bitfield cases,
signal trampoline names, _sgtk_* helpers, __result/__ptr temporaries,
hardcoded G_TYPE_* GValue constants) and drop generated block comments to
reach zero lint findings across all 6 tiers.
