feat(sw): implement SW header design system

src/sw/assets/sw-header-logo-placeholder.svg

@@ -0,0 +1,7 @@
+<!-- TEMPORARY placeholder for the SW Header logo slot (Storybook only). Not a product logo. -->
+<svg xmlns="http://www.w3.org/2000/svg" width="64" height="34" viewBox="0 0 64 34" fill="none">
+  <rect x="1" y="1" width="62" height="32" rx="5" stroke="#F0F7F5" stroke-opacity="0.55" stroke-width="2" stroke-dasharray="5 4"/>
+  <circle cx="18" cy="17" r="7" fill="#F0F7F5" fill-opacity="0.55"/>
+  <rect x="30" y="11" width="22" height="4" rx="2" fill="#F0F7F5" fill-opacity="0.55"/>
+  <rect x="30" y="19" width="14" height="4" rx="2" fill="#F0F7F5" fill-opacity="0.35"/>
+</svg>