perf(settings): write config on release instead of every slider frame

ImGui sliders report a change in every frame the value moves, so dragging one
rewrote the full 31 KB config to disk per frame -- serialize, fsync and rename,
synchronously on the draw thread. Measured on Linux/Wine that showed up as a
114 ms frame while the plugin itself only drew for 2.9 ms; the rest was waiting
on the write.

The five shared slider helpers now defer SaveConfig to IsItemDeactivatedAfterEdit,
matching what ChatColourPicker already did for the colour wheel.

Renaming a tab needed its own path: the input lives inside a popup, and ImGui
never re-submits it when the popup is dismissed by clicking outside, so
IsItemDeactivatedAfterEdit would not fire and the new name would be lost. A
pending-rename marker scoped to the owning tab flushes it when the popup is
gone -- scoped, because every other tab's Draw reaches that branch too.

DeferredSaveFrames is removed: the debounce was fully wired but never armed,
and this approach makes it redundant.

HellionChat/Plugin.cs

@@ -175,8 +175,6 @@ public sealed class Plugin : IAsyncDalamudPlugin
     // PerformanceBaselineStep so the hot path stays allocation-free.
     internal double LastDrawMs;
 
-    internal int DeferredSaveFrames = -1;
-
     // Cancels the v1.4.8 FTS5 bulk-insert worker on plugin teardown. The
     // worker runs off the framework thread on its own SqliteConnection, so a
     // Dispose mid-rebuild must signal cancellation before MessageManager
@@ -277,8 +275,6 @@ public sealed class Plugin : IAsyncDalamudPlugin
 
         ImGuiUtil.Initialize(this);
 
-        DeferredSaveFrames = -1;
-
         // Custom themes dir + seed run before the container builds so the
         // ThemeRegistry factory lambda finds the directory ready.
         var customThemesDir = Path.Combine(Interface.ConfigDirectory.FullName, "themes");
@@ -641,19 +637,6 @@ public sealed class Plugin : IAsyncDalamudPlugin
             }
         );
 
-        // Flush a pending DeferredSave — FrameworkUpdate won't fire it anymore.
-        failure = CaptureFailure(
-            failure,
-            () =>
-            {
-                if (DeferredSaveFrames >= 0)
-                {
-                    SaveConfig();
-                    DeferredSaveFrames = -1;
-                }
-            }
-        );
-
         // Framework-thread cleanup the container does not reach.
         try
         {
@@ -1134,9 +1117,6 @@ public sealed class Plugin : IAsyncDalamudPlugin
 
     private void FrameworkUpdate(IFramework framework)
     {
-        if (DeferredSaveFrames >= 0 && DeferredSaveFrames-- == 0)
-            SaveConfig();
-
         if (!Config.HideChat)
             return;