Handle legacy single-object manyDecks config

Old configs have manyDecks as a plain object; new format is an array.
Wrap the old format in an array so existing deployments keep working
without a config migration.

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

server/src/ts/config.ts

@@ -171,7 +171,12 @@ const parseManyDecks = (
 const parseSources = (sources: BaseSources<UnparsedDuration>): Sources => ({
   ...(sources.builtIn !== undefined ? { builtIn: sources.builtIn } : {}),
   ...(sources.manyDecks !== undefined
-    ? { manyDecks: sources.manyDecks.map(parseManyDecks) }
+    ? {
+        manyDecks: (Array.isArray(sources.manyDecks)
+          ? sources.manyDecks
+          : [sources.manyDecks]
+        ).map(parseManyDecks),
+      }
     : {}),
   ...(sources.jsonAgainstHumanity !== undefined
     ? { jsonAgainstHumanity: sources.jsonAgainstHumanity }