Q-W1 code-review follow-ups: restore 104 trailing newlines, relocate reasampler_uid.h to core/wire, drop ext_keys namespaces shim, add slot_map_tests, golden serialize literals for 4 modules, namespaces.h/pragma-once ordering sweep. 60/60 green.

src/core/ui/overflow_menu.cpp

@@ -39,4 +39,4 @@ bool hitTestMenuButton(int px, int py, const MenuButtonRect& button) {
            py >= button.y && py < button.y + button.height;
 }
 
-} // namespace reasampler::ui
+} // namespace reasampler::ui