style(storybook): group overlay, disclosure and navigation story pages

- Sheet + Drawer, Tooltip + Hover Card, Accordion + Collapsible,
  Dialog + Alert Dialog, Dropdown Menu + Context Menu on one page each
  (specimens moved to *-examples.tsx; absorbed Stories keep their IDs)
- Popover, Tabs content spacing, Breadcrumb, Menubar and Command tidied
- Component docs updated to the new representative pages

src/components/menubar.stories.tsx

@@ -37,7 +37,7 @@ function Specimen() {
           <MenubarItem>
             열기 <MenubarShortcut>⌘O</MenubarShortcut>
           </MenubarItem>
-          <MenubarItem disabled>저장 (사용 불가)</MenubarItem>
+          <MenubarItem disabled>저장</MenubarItem>
           <MenubarSeparator />
           <MenubarSub>
             <MenubarSubTrigger>내보내기</MenubarSubTrigger>