refactor(sw): share roving focus and outside pointer handling

- components/shared/roving-focus.ts (moveRovingFocus): the same Arrow / Home / End algorithm of SWFooter, SWToolGroup,
  the SWViewerHeader tabs and SWHomeMenu; each caller passes its own keys, wrap and select behavior.
- components/shared/use-outside-pointer.ts (useOutsidePointerDown): the same pointerdown effect of the SWHeader
  dropdowns, layer menu, document title and More. Escape, focus return and positioning stay in each component.
Both modules are internal: the package entry and the public declarations are unchanged.

packages/sw/src/components/shared/roving-focus.ts

@@ -0,0 +1,20 @@
+import type { KeyboardEvent } from "react"
+
+/**
+ * Internal (not exported from the package): roving focus among `items`, shared by SWFooter, SWToolGroup, the
+ * SWViewerHeader tabs and SWHomeMenu (2026-10-20; the four copies had the same algorithm). ArrowRight / ArrowLeft —
+ * and ArrowDown / ArrowUp when `vertical` — move and wrap; Home / End jump. Nothing happens unless the focused element
+ * is one of `items`. `select` clicks the new item (radio groups). Returns whether the key was handled.
+ */
+export function moveRovingFocus(event: KeyboardEvent<HTMLElement>, items: HTMLElement[], { vertical = false, select = false } = {}) {
+  const forward = event.key === "ArrowRight" || (vertical && event.key === "ArrowDown")
+  const backward = event.key === "ArrowLeft" || (vertical && event.key === "ArrowUp")
+  if (!forward && !backward && event.key !== "Home" && event.key !== "End") return false
+  const index = items.indexOf(document.activeElement as HTMLElement)
+  if (index < 0) return false
+  event.preventDefault()
+  const next = event.key === "Home" ? 0 : event.key === "End" ? items.length - 1 : (index + (forward ? 1 : -1) + items.length) % items.length
+  items[next].focus()
+  if (select) items[next].click()
+  return true
+}

packages/sw/src/components/shared/use-outside-pointer.ts

@@ -0,0 +1,19 @@
+import { useEffect, useRef, type RefObject } from "react"
+
+/**
+ * Internal (not exported from the package): while `open`, a pointerdown outside `rootRef` calls `onOutside` (the latest
+ * one). Shared by the SWHeader dropdowns, layer menu, document title and More (2026-10-20; the four copies were the same
+ * effect). Escape, focus return and positioning stay in each component.
+ */
+export function useOutsidePointerDown(open: boolean, rootRef: RefObject<HTMLElement | null>, onOutside: () => void) {
+  const latest = useRef(onOutside)
+  latest.current = onOutside
+  useEffect(() => {
+    if (!open) return
+    const onPointerDown = (event: PointerEvent) => {
+      if (!rootRef.current?.contains(event.target as Node)) latest.current()
+    }
+    document.addEventListener("pointerdown", onPointerDown)
+    return () => document.removeEventListener("pointerdown", onPointerDown)
+  }, [open, rootRef])
+}