refactor: improve string representation for countries

- Update links in cities index to include country emoji
- Modify display in cities show view to use emoji and country name
- Clean up random scope method in weather_art model for consistency

These changes enhance the user interface presentation by making
country names visually enriched with emojis, improving the overall
user experience with clearer visual cues.

app/models/weather_art.rb

@@ -34,13 +34,13 @@ class WeatherArt < ApplicationRecord
   scope :random, ->(limit = 3) {
     if ActiveRecord::Base.connection.adapter_name.downcase == "postgresql"
       # PostgreSQL 优化版本
-      order(Arel.sql('RANDOM()')).limit(limit)
+      order(Arel.sql("RANDOM()")).limit(limit)
     elsif ActiveRecord::Base.connection.adapter_name.downcase == "mysql2"
       # MySQL 优化版本
-      order(Arel.sql('RAND()')).limit(limit)
+      order(Arel.sql("RAND()")).limit(limit)
     else
       # SQLite 或其他数据库的通用版本
-      order(Arel.sql('RANDOM()')).limit(limit)
+      order(Arel.sql("RANDOM()")).limit(limit)
     end
   }
 

app/views/cities/index.html.erb

@@ -93,7 +93,7 @@
                 <div class="divider my-1"></div>
                 <% @current_region.countries.order(:name).each do |country| %>
                   <li>
-                    <%= link_to country.name,
+                    <%= link_to "#{country&.emoji + " " || ""}#{country.name}",
                                 cities_path(region: @current_region.slug, country: country.slug),
                                 class: "#{@current_country == country ? 'active' : ''}" %>
                   </li>

app/views/cities/show.html.erb

@@ -32,7 +32,7 @@
 
         <div class="flex flex-wrap justify-center items-center gap-3">
           <div class="badge badge-lg badge-primary gap-2">
-            <%= @city.country.name %>, <%= @city.region %>
+            <%= "#{@city&.country&.emoji + " " || ""}#{@city&.country&.name}" %>, <%= @city.region %>
           </div>
           <div class="badge badge-lg badge-secondary gap-2">
             <%= @city.timezone.present? ? Time.current.in_time_zone(@city.timezone).strftime("%Y-%m-%d %H:%M") : "Timezone undefined" %>