feat(config): bump schema to v20 with style-refactor visibility fields

Adds MainWindowOpen, SettingsWindowOpen, MaxParallelPopouts (channel popout
pool size), TellAutoOpenMode (Off/Sidebar/TopTab/Popout) and
SidebarAutoSwitchThresholdPx. Migration is additive — field initializers
fill defaults for v19 configs, the Plugin.cs schema gate bumps the version
stamp after load. UpdateFrom gets explicit sync statements for all five so
settings-save edits do not drop them.

HellionChat/Configuration.cs

@@ -35,7 +35,7 @@ public class ConfigKeyBind
 [Serializable]
 public class Configuration : IPluginConfiguration
 {
-    private const int LatestVersion = 19;
+    private const int LatestVersion = 20;
 
     public int Version { get; set; } = LatestVersion;
 
@@ -252,6 +252,15 @@ public class Configuration : IPluginConfiguration
     public ConfigKeyBind? ChatTabForward;
     public ConfigKeyBind? ChatTabBackward;
 
+    // v20 fields: window visibility state, channel popout pool size and
+    // sidebar auto-switch threshold. All initializers double as the
+    // migration defaults for configs loaded at v19 or earlier.
+    public bool MainWindowOpen = true;
+    public bool SettingsWindowOpen;
+    public int MaxParallelPopouts = 8;
+    public TellAutoOpenMode TellAutoOpenMode = TellAutoOpenMode.Sidebar;
+    public int SidebarAutoSwitchThresholdPx = 800;
+
     public void UpdateFrom(Configuration other, bool backToOriginal)
     {
         if (backToOriginal)
@@ -392,9 +401,24 @@ public class Configuration : IPluginConfiguration
 
         WorldSuffixMode = other.WorldSuffixMode;
         NameFormMode = other.NameFormMode;
+
+        MainWindowOpen = other.MainWindowOpen;
+        SettingsWindowOpen = other.SettingsWindowOpen;
+        MaxParallelPopouts = other.MaxParallelPopouts;
+        TellAutoOpenMode = other.TellAutoOpenMode;
+        SidebarAutoSwitchThresholdPx = other.SidebarAutoSwitchThresholdPx;
     }
 }
 
+[Serializable]
+public enum TellAutoOpenMode
+{
+    Off,
+    Sidebar,
+    TopTab,
+    Popout,
+}
+
 [Serializable]
 public enum UnreadMode
 {

HellionChat/Plugin.cs

@@ -200,11 +200,12 @@ public sealed class Plugin : IAsyncDalamudPlugin
         // do not touch either static, so the brief null-window is safe.
 
         // Schema gate: v1.4.x+ requires config v16+. Users on older schemas
-        // must install v1.4.2 first to run the migration chain. v19 adds the
+        // must install v1.4.2 first to run the migration chain. v19 added the
         // top-level CustomSoundVolume, WindowOpacityInactive, WorldSuffixMode
-        // and NameFormMode fields — all additive with defaults, so v16-v18
+        // and NameFormMode fields; v20 adds MainWindowOpen, SettingsWindowOpen,
-        // configs load cleanly and get their Version stamp bumped after the
+        // MaxParallelPopouts, TellAutoOpenMode and SidebarAutoSwitchThresholdPx
-        // gate.
+        // — all additive with defaults, so v16-v19 configs load cleanly and
+        // get their Version stamp bumped after the gate.
         if (Config.Version < 16)
         {
             throw new InvalidOperationException(
@@ -212,7 +213,7 @@ public sealed class Plugin : IAsyncDalamudPlugin
                     + "Please install v1.4.2 first to migrate the configuration, then upgrade to v1.4.10."
             );
         }
-        Config.Version = 19;
+        Config.Version = 20;
 
         // Unpinned TempTabs are session-only and dropped on every load. Pinned
         // TempTabs survive reload — Jin's tester feedback (v1.4.7).