FIX: Update mobile logo resolution

This makes Discourse compliant with latest Google PWA requirements,
so we get the App Install banner back.

Should bump our Lighthouse PWA Audit score to 11/11.

app/controllers/metadata_controller.rb

@@ -13,6 +13,8 @@ def opensearch
   private
 
   def default_manifest
+    logo = SiteSetting.mobile_logo_url || SiteSetting.logo_small_url || SiteSetting.apple_touch_icon_url
+
     manifest = {
       name: SiteSetting.title,
       short_name: SiteSetting.title,
@@ -23,8 +25,8 @@ def default_manifest
       theme_color: "##{ColorScheme.hex_for_name('header_background')}",
       icons: [
         {
-          src: SiteSetting.apple_touch_icon_url,
-          sizes: "144x144",
+          src: logo,
+          sizes: "512x512",
           type: "image/png"
         }
       ]

config/locales/server.en.yml

@@ -1011,7 +1011,7 @@ en:
     digest_logo_url: "The alternate logo image used at the top of your site's email summary. Should be a wide rectangle shape. Should not be an SVG image. If left blank `logo_url` will be used."
     logo_small_url: "The small logo image at the top left of your site, should be a square shape, seen when scrolling down. If left blank a home glyph will be shown."
     favicon_url: "A favicon for your site, see http://en.wikipedia.org/wiki/Favicon, to work correctly over a CDN it must be a png"
-    mobile_logo_url: "The fixed position logo image used at the top left of your mobile site. Should be a square shape. If left blank, `logo_url` will be used. eg: http://example.com/uploads/default/logo.png"
+    mobile_logo_url: "The fixed position logo image used at the top left of your mobile site and as your logo/splash image on Android. Recommended size is 512px by 512px. If left blank, `logo_url` will be used. eg: http://example.com/uploads/default/logo.png"
     apple_touch_icon_url: "Icon used for Apple touch devices. Recommended size is 144px by 144px."
 
     notification_email: "The from: email address used when sending all essential system emails. The domain specified here must have SPF, DKIM and reverse PTR records set correctly for email to arrive."