chore(qt): vendor the country flag set used by the artist scene

265 SVG flags (1.1 MB) plus the upstream MIT licence and attribution in
crates/qbz-qt/third-party/. Kept as its own commit so the asset drop can be
rolled back or re-sourced without touching the scene code that consumes it.

cc

crates/qbz-qt/qml/assets/flags/fx.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="512" height="512" viewBox="0 0 512 512"><mask id="a"><circle cx="256" cy="256" r="256" fill="#fff"/></mask><g mask="url(#a)"><path fill="#eee" d="M167 0h178l25.9 252.3L345 512H167l-29.8-253.4z"/><path fill="#0052b4" d="M0 0h167v512H0z"/><path fill="#d80027" d="M345 0h167v512H345z"/></g></svg>