feat(sidebar): pinned section, dimmed pin glyph, configurable width

Smoke-test round 3 feedback from Jin:

- Sidebar now groups tabs into three sections rendered in this order:
  persistent → pinned TempTabs → unpinned TempTabs. Each TempTab
  section carries its own divider header ("Angepinnt (n)" / "Aktive
  Tells (n)"). Plugin.Config.Tabs order is untouched — only the
  display order changes, so tabI still mirrors the real index and
  LastTab/WantedTab stay consistent.

- The thumbtack glyph overlay on a pinned tab dropped from accent
  colour at full alpha to TextMuted at ~47% alpha. The section header
  is now the primary discoverability cue; the glyph is just a per-tab
  confirmation hint.

- Sidebar width is now a Config field (default 44, range 44-160).
  Slider lives in Theme & Layout under the existing Sidebar-Tab-View
  toggle. The icon button inside each row stretches with the width so
  a widened sidebar doesn't leave the icon floating in dead space.

HellionChat/Ui/SettingsTabs/ThemeAndLayout.cs

@@ -250,6 +250,26 @@ internal sealed class ThemeAndLayout : ISettingsTab
                 string.Format(Language.Options_SidebarTabView_Description, Plugin.PluginName)
             );
 
+            if (Mutable.SidebarTabView)
+            {
+                var sidebarWidth = Mutable.SidebarWidth;
+                if (
+                    ImGui.SliderInt(
+                        HellionStrings.Settings_ThemeAndLayout_SidebarWidth_Name,
+                        ref sidebarWidth,
+                        44,
+                        160,
+                        $"{sidebarWidth} px"
+                    )
+                )
+                {
+                    Mutable.SidebarWidth = sidebarWidth;
+                }
+                ImGuiUtil.HelpMarker(
+                    HellionStrings.Settings_ThemeAndLayout_SidebarWidth_Description
+                );
+            }
+
             ImGui.Spacing();
             ImGui.Separator();
             ImGui.Spacing();