Welcome modal on logged-out homepage (#8944)

* Adds welcome modal to logged-out homepage

* Adds metrics and feature gate for welcome modal

* Slightly smaller text for mobile screens to avoid wrapping

* Remove unused SVG

* Adds text gradient and "X" close button

* Fix color on "Already have an account?" text

* tweak hooks, react import

* rm stylesheet

* use hardcoded colors

* add focus guards and scope

* no such thing as /home

* reduce spacign

* use css animations

* use session storage

* fix animation fill mode

* add a11y props

* Fix link/button color mismatch, reduce gap between buttons, show modal until user dismisses it

* Fix "Already have an account?" line left-aligning in small window sizes

* Adds "dismissed" and "presented" metric events

---------

Co-authored-by: Samuel Newman <mozzius@protonmail.com>

src/view/shell/index.web.tsx

@@ -8,6 +8,7 @@ import {RemoveScrollBar} from 'react-remove-scroll-bar'
 import {useIntentHandler} from '#/lib/hooks/useIntentHandler'
 import {useWebMediaQueries} from '#/lib/hooks/useWebMediaQueries'
 import {type NavigationProp} from '#/lib/routes/types'
+import {useGate} from '#/lib/statsig/statsig'
 import {useGeolocation} from '#/state/geolocation'
 import {useIsDrawerOpen, useSetDrawerOpen} from '#/state/shell'
 import {useComposerKeyboardShortcut} from '#/state/shell/composer/useComposerKeyboardShortcut'
@@ -22,11 +23,13 @@ import {EmailDialog} from '#/components/dialogs/EmailDialog'
 import {LinkWarningDialog} from '#/components/dialogs/LinkWarning'
 import {MutedWordsDialog} from '#/components/dialogs/MutedWords'
 import {SigninDialog} from '#/components/dialogs/Signin'
+import {useWelcomeModal} from '#/components/hooks/useWelcomeModal'
 import {
   Outlet as PolicyUpdateOverlayPortalOutlet,
   usePolicyUpdateContext,
 } from '#/components/PolicyUpdateOverlay'
 import {Outlet as PortalOutlet} from '#/components/Portal'
+import {WelcomeModal} from '#/components/WelcomeModal'
 import {FlatNavigator, RoutesContainer} from '#/Navigation'
 import {Composer} from './Composer.web'
 import {DrawerContent} from './Drawer'
@@ -42,6 +45,8 @@ function ShellInner() {
   const showDrawer = !isDesktop && isDrawerOpen
   const [showDrawerDelayedExit, setShowDrawerDelayedExit] = useState(showDrawer)
   const {state: policyUpdateState} = usePolicyUpdateContext()
+  const welcomeModalControl = useWelcomeModal()
+  const gate = useGate()
 
   useLayoutEffect(() => {
     if (showDrawer !== showDrawerDelayedExit) {
@@ -80,6 +85,11 @@ function ShellInner() {
       <LinkWarningDialog />
       <Lightbox />
 
+      {/* Show welcome modal if the gate is enabled */}
+      {welcomeModalControl.isOpen && gate('welcome_modal') && (
+        <WelcomeModal control={welcomeModalControl} />
+      )}
+
       {/* Until policy update has been completed by the user, don't render anything that is portaled */}
       {policyUpdateState.completed && (
         <>