feat(settings): toggle for the symbol-picker chat-input button

Adds a Configuration property, defaulted to enabled, and a checkbox in
the Chat settings tab's Behaviour section. Strings live in HellionStrings
so DE/EN stays in sync. Defaults aligned with our 'discoverable by
default, hidden by user choice' convention. Schema stays at v17 — the
new boolean is additive, the default constructor covers existing configs.

HellionChat/Ui/ChatLogWindow.cs

@@ -799,13 +799,19 @@ public sealed class ChatLogWindow : Window
         // inside DrawAndConsume pins to the last rendered item, so the call MUST
         // run immediately after this IconButton — placing it after the channel
         // picker below would pin the popup under the wrong widget.
-        if (ImGuiUtil.IconButton(
-                FontAwesomeIcon.Smile,
-                "symbol-picker-trigger",
-                "Insert symbol or FFXIV icon"))
+        if (Plugin.Config.SymbolPickerEnabled)
         {
-            _symbolPicker.OpenPopup();
+            if (ImGuiUtil.IconButton(
+                    FontAwesomeIcon.Smile,
+                    "symbol-picker-trigger",
+                    "Insert symbol or FFXIV icon"))
+            {
+                _symbolPicker.OpenPopup();
+            }
         }
+        // DrawAndConsume runs unconditionally; with the button hidden the popup
+        // can't open, so the call is a no-op. Splice path stays outside the
+        // guard for the same reason.
         var insertedSymbol = _symbolPicker.DrawAndConsume();
         if (insertedSymbol is not null)
         {
@@ -817,7 +823,8 @@ public sealed class ChatLogWindow : Window
             Activate = true;
             ActivatePos = pos + insertedSymbol.Length;
         }
-        ImGui.SameLine();
+        if (Plugin.Config.SymbolPickerEnabled)
+            ImGui.SameLine();
 
         var beforeIcon = ImGui.GetCursorPos();