feat(sw): viewer mode header, dropdown and popup panel

- SWViewerHeader: data-driven viewer menu (button / toggle / menu / tabs / switch / custom), More by
  collapseBelow, trailing slot, onCommand; SWHeader logo props with no default logo
- SWViewerMenu: dropdown, check / radio, multi-level submenu, context menu at a point
- SWViewerPanel: viewer popup frame with free children / footer, drag, corner resize, collapse, modal
- Panel controls: SWViewerSection / Field / Hint / Switch / Slider / Input / Button / Badge / Status
- SWHeader black text outline tokens on viewer text, matching icon outline (drop-shadow)
- Storybook SW/Viewer stories; remove SW/Tool story (SW/Popup kept)
- AI guide ai/VIEWER.md, example H, verification scripts and evidence

packages/sw/src/index.ts

@@ -10,3 +10,6 @@ export {
   SWPopup, SWPopupSection, SWPopupRow,
   type SWPopupProps, type SWPopupSectionProps, type SWPopupRowProps,
 } from "./components/sw-popup/SWPopup"
+
+// SW viewer mode (2026-10-19): viewer header, dropdown, popup panel and panel controls.
+export * from "./components/sw-viewer"