iPadOS 13+ Safari reports a macOS user-agent by default, so
ua-parser-js sees os.name === 'Mac OS' and leaves device.type
unset. mobileOrTablet() already handles this via maxTouchPoints > 1,
but three layout gates only checked screenSize === ScreenSize.Mobile
(which is width-based, so a full-width iPad reads as Desktop or Tablet):

- MobileFriendlyPageNav: hides the sidebar when a room is active
- MobileFriendlyClientNav: hides the app nav bar when deep in a route
- createRouter: adds a WelcomePage index route instead of an empty outlet
- PageRoot: suppresses the vertical divider line between nav and content

All four now also check mobileOrTablet() so iPads in desktop-UA mode
get the correct single-panel navigation behaviour.

…Website' mode

Replaces mobileOrTablet() with mobileOrTabletLayout() for all layout
decisions in Home, Direct, Space, Explore, and Inbox page components.

mobileOrTablet() returns true for all tablets (including iPad with native
UA or 'Request Desktop Website'), so isMobile was true on iPad, causing
the room list nav to render at width 100% with no resize handle — giving
a broken half-layout where the sidebar took the full width.

mobileOrTabletLayout() is true only for phone-form-factor devices, so
tablets always get the fixed-width desktop sidebar and SidebarResizer.

Space.tsx retains mobileOrTablet() for the swipe-to-room touch gesture,
which is appropriate for all touch devices including tablets.