add barebones theme switcher

app/__init__.py

@@ -2,7 +2,7 @@ from flask import Flask, session
 from dotenv import load_dotenv
 from .models import Avatars, Users, PostHistory, Posts
 from .auth import digest
-from .routes.users import is_logged_in, get_active_user
+from .routes.users import is_logged_in, get_active_user, get_prefers_theme
 from .routes.threads import get_post_url
 from .constants import (
     PermissionLevel, permission_level_string,
@@ -140,6 +140,7 @@ def create_app():
     def inject_funcs():
         return {
             'get_post_url': get_post_url,
+            'get_prefers_theme': get_prefers_theme,
         }
 
     @app.template_filter("ts_datetime")