Fix Guest should also have auto mode by default

This is still under feature flag. But guest should have auto theme
mode set as default. It's default for every user.

Release-Notes: skip
Change-Id: Ia68529be5a0280fd38ac7943275b4b8842ded0f3
diff --git a/polygerrit-ui/app/constants/constants.ts b/polygerrit-ui/app/constants/constants.ts
index 503c35a..99f7606 100644
--- a/polygerrit-ui/app/constants/constants.ts
+++ b/polygerrit-ui/app/constants/constants.ts
@@ -264,7 +264,7 @@
     diff_view: DiffViewMode.SIDE_BY_SIDE,
     size_bar_in_change_table: true,
     my: [],
-    theme: AppTheme.LIGHT,
+    theme: AppTheme.AUTO,
     date_format: DateFormat.EURO,
     time_format: TimeFormat.HHMM_24,
     change_table: [],