#435 web dark mode (#455)

* add ThemeProvider to App.web.tsx

* make FlatNavigator use themed color

* fix extra padding on top in web

* add observer to App.web.tsx to make it react to theme changes

* fix TS for useColorSchemeStyle

* add dark mode toggle button to web LeftNav

* fix index.web.tsx border colors for web

* Move the darkmode desktop web toggle to the right nav column

---------

Co-authored-by: Paul Frazee <pfrazee@gmail.com>

src/view/shell/desktop/LeftNav.tsx

@@ -130,7 +130,7 @@ export const DesktopLeftNav = observer(function DesktopLeftNav() {
   const pal = usePalette('default')
 
   return (
-    <View style={styles.leftNav}>
+    <View style={[styles.leftNav, pal.view]}>
       {store.session.hasSession && <ProfileCard />}
       <BackBtn />
       <NavItem
@@ -246,6 +246,7 @@ const styles = StyleSheet.create({
     paddingHorizontal: 16,
     backgroundColor: colors.blue3,
     marginTop: 20,
+    marginBottom: 10,
   },
   newPostBtnIconWrapper: {
     marginRight: 8,