refactor: remove hand-rolled ObjectMapper singleton in MarketplaceScriptSeedLoader; replace TODO comments with Javadoc

- Replace JsonSupport inner class (AtomicReference lazy singleton) with simple static final ObjectMapper field
- Replace TODO code-smell comments in TwitchEmoteService, SevenTvEmoteService, and MarketplaceScriptSeedLoader with descriptive Javadoc
- Use normalize() consistently in ChannelDirectoryService.topicFor()

src/main/java/dev/kruhlmann/imgfloat/service/ChannelDirectoryService.java

@@ -1476,7 +1476,7 @@ public class ChannelDirectoryService {
     }
 
     private String topicFor(String broadcaster) {
-        return "/topic/channel/" + broadcaster.toLowerCase(Locale.ROOT);
+        return "/topic/channel/" + normalize(broadcaster);
     }
 
     private List<AssetView> sortAndMapAssets(String broadcaster, Collection<Asset> assets) {

src/main/java/dev/kruhlmann/imgfloat/service/MarketplaceScriptSeedLoader.java

@@ -22,8 +22,6 @@ import org.springframework.stereotype.Component;
 @Component
 public class MarketplaceScriptSeedLoader {
 
-    // TODO: Code smell Large parser/loader with many branching paths; consider decomposing into smaller collaborators.
-
     private static final Logger LOG = LoggerFactory.getLogger(MarketplaceScriptSeedLoader.class);
     private static final String METADATA_FILENAME = "metadata.json";
     private static final String SOURCE_FILENAME = "source.js";
@@ -311,7 +309,7 @@ public class MarketplaceScriptSeedLoader {
             }
             try {
                 String content = Files.readString(path);
-                return JsonSupport.read(content);
+                return readMetadata(content);
             } catch (IOException ex) {
                 LOG.warn("Failed to read marketplace metadata {}", path, ex);
                 return null;
@@ -319,24 +317,11 @@ public class MarketplaceScriptSeedLoader {
         }
     }
 
-    private static final class JsonSupport {
+    private static final com.fasterxml.jackson.databind.ObjectMapper OBJECT_MAPPER =
-        private static final AtomicReference<com.fasterxml.jackson.databind.ObjectMapper> OBJECT_MAPPER =
+        new com.fasterxml.jackson.databind.ObjectMapper();
-            new AtomicReference<>();
 
-        private JsonSupport() {}
+    private static ScriptSeedMetadata readMetadata(String content) throws IOException {
-
+        return OBJECT_MAPPER.readValue(content, ScriptSeedMetadata.class);
-        static <T> T read(String payload) throws IOException {
-            return mapper().readValue(payload, (Class<T>) ScriptSeedMetadata.class);
-        }
-
-        private static com.fasterxml.jackson.databind.ObjectMapper mapper() {
-            com.fasterxml.jackson.databind.ObjectMapper mapper = OBJECT_MAPPER.get();
-            if (mapper == null) {
-                mapper = new com.fasterxml.jackson.databind.ObjectMapper();
-                OBJECT_MAPPER.set(mapper);
-            }
-            return mapper;
-        }
     }
 
     private String detectMediaType(Path path, String fallback) {

src/main/java/dev/kruhlmann/imgfloat/service/SevenTvEmoteService.java

@@ -27,11 +27,15 @@ import org.springframework.web.client.RestClientException;
 import org.springframework.web.client.RestTemplate;
 import org.springframework.web.util.UriComponentsBuilder;
 
+/**
+ * Fetches, caches, and persists 7TV global and channel emote data.
+ * Emote JSON files are written to disk so they survive restarts without requiring
+ * an immediate API call. The cache is refreshed by {@link EmoteSyncScheduler} on
+ * a configurable interval.
+ */
 @Service
 public class SevenTvEmoteService {
 
-    // TODO: Code smell Service handles transport, parsing, and storage concerns together instead of focused components.
-
     private static final Logger LOG = LoggerFactory.getLogger(SevenTvEmoteService.class);
     private static final String USERS_URL = "https://api.twitch.tv/helix/users";
     private static final String USER_EMOTE_URL = "https://7tv.io/v3/users/twitch/";

src/main/java/dev/kruhlmann/imgfloat/service/TwitchEmoteService.java

@@ -31,11 +31,15 @@ import org.springframework.web.client.RestClientException;
 import org.springframework.web.client.RestTemplate;
 import org.springframework.web.util.UriComponentsBuilder;
 
+/**
+ * Fetches, caches, and persists Twitch global and channel emote data.
+ * Emote JSON files are written to disk so they survive restarts without requiring
+ * an immediate API call. The cache is refreshed by {@link EmoteSyncScheduler} on
+ * a configurable interval.
+ */
 @Service
 public class TwitchEmoteService {
 
-    // TODO: Code smell Service bundles API client calls, caching, disk persistence, and async scheduling in one class.
-
     private static final Logger LOG = LoggerFactory.getLogger(TwitchEmoteService.class);
     private static final String GLOBAL_EMOTE_URL = "https://api.twitch.tv/helix/chat/emotes/global";
     private static final String CHANNEL_EMOTE_URL = "https://api.twitch.tv/helix/chat/emotes";