feat(privacy): default PrivacyPersistUnknownChannels to true for new configs

F3.1: future FFXIV patches can add new ChatTypes that aren't on any
existing whitelist. With the field defaulted to false a new install
would silently drop those channels until the user opts in. New configs
now start with PrivacyPersistUnknownChannels=true via a constant in
PrivacyDefaults. Existing configs keep their explicit choice — the
deserializer overrides the initializer, so no migration and no schema
bump.

HellionChat/Configuration.cs

@@ -57,8 +57,12 @@ public class Configuration : IPluginConfiguration
     // Empty set means the migration has not run yet — see Plugin.cs v6→v7.
     public HashSet<ChatType> PrivacyPersistChannels = [];
 
-    // Failsafe for ChatTypes added by future FFXIV patches.
+    // Failsafe for ChatTypes added by future FFXIV patches. New configs default
-    public bool PrivacyPersistUnknownChannels;
+    // to the failsafe via PrivacyDefaults; existing configs keep their saved
+    // choice because the deserializer overrides this initializer.
+    public bool PrivacyPersistUnknownChannels = Privacy
+        .PrivacyDefaults
+        .DefaultPersistUnknownChannels;
 
     public bool IsAllowedForStorage(ChatType type)
     {

HellionChat/Privacy/PrivacyDefaults.cs

@@ -4,6 +4,12 @@ namespace HellionChat.Privacy;
 
 internal static class PrivacyDefaults
 {
+    // F3.1: failsafe for ChatTypes added by future FFXIV patches. New installs
+    // persist unknown channels so a major patch's added ChatType isn't silently
+    // dropped before the user can opt in or out. Existing configs keep their
+    // explicit choice — see Configuration.cs PrivacyPersistUnknownChannels.
+    internal const bool DefaultPersistUnknownChannels = true;
+
     // DSGVO Art. 25 (Privacy by Default): only the player's own conversations
     // are persisted out-of-the-box. Public chat, NPC dialogue, system logs and
     // battle messages require explicit opt-in.