feat: add admin settings system and improve customer/pricing endpoints

Add centralized admin settings (company info, social links, quick calls,
sidebar visibility toggles, theme, logo upload) with singleton pattern
and full CRUD API. Add active/dedicated customer count endpoints for
dashboard stats. Fix automatic assignment route to use PUT instead of
GET. Refactor oil price endpoint to use schema serialization with null
safety.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/info/views.py

@@ -52,14 +52,10 @@ def get_oil_price_today():
                      .query(Pricing_Oil_Oil)
                      .order_by(Pricing_Oil_Oil.date.desc())
                      .first())
-    return success_response({
-        'price_from_supplier': get_price_query.price_from_supplier,
-        'price_for_customer': get_price_query.price_for_customer,
-        'price_for_employee': get_price_query.price_for_employee,
-        'price_same_day': get_price_query.price_same_day,
-        'price_prime': get_price_query.price_prime,
-        'price_emergency': get_price_query.price_emergency,
-    })
+    if get_price_query:
+        delivery_schema = Pricing_Oil_Oil_schema(many=False)
+        return success_response(delivery_schema.dump(get_price_query))
+    return error_response("No pricing data found", 404)
 
 
 @info.route("/price/oil/table", methods=["GET"])