fix(v0.5.0): pre-release polish from full-codebase review

- Plugin.cs: mark RetentionSweepRunning volatile so the ImGui thread
  reads the latest value without a stale register-cached copy
- EmoteCache.cs: reset State to Unloaded on exception so a later
  trigger can retry instead of being blocked by the early-out
- Settings.cs: switch the SaveAndClose / Discard buttons to Allman
  bracing for consistency with the rest of the file, and include the
  ItemSpacing in the Ko-fi-button right-edge calculation
- Privacy.cs: add a saved-policy hint above the manual retention
  Ctrl+Shift button so the existing Cleanup wording pattern is
  matched here too
- HellionStrings: drop seven unreferenced keys (Theme_Heading,
  Migration_Notification_*, Migration_Webinterface_Removed_*,
  AutoTellTabs_Migration_*) and their EN/DE values, add the new
  Retention_Help_SavedNote string

ChatTwo/Resources/HellionStrings.resx

@@ -78,6 +78,9 @@
   <data name="Cleanup_Help_SavedNote" xml:space="preserve">
     <value>Cleanup uses your SAVED whitelist (Plugin.Config), not unsaved edits above. Click Save first if you want to apply your current edits.</value>
   </data>
+  <data name="Retention_Help_SavedNote" xml:space="preserve">
+    <value>The manual sweep uses your SAVED retention policy, not the slider values above. Click Save first if you want the run to apply your current edits.</value>
+  </data>
   <data name="Cleanup_RefreshPreview" xml:space="preserve">
     <value>Refresh preview</value>
   </data>
@@ -177,18 +180,6 @@
   <data name="Retention_Error" xml:space="preserve">
     <value>Retention sweep failed, see /xllog</value>
   </data>
-  <data name="Migration_Notification_Title" xml:space="preserve">
-    <value>Hellion Chat</value>
-  </data>
-  <data name="Migration_Notification_Content" xml:space="preserve">
-    <value>Privacy filter activated by default. Settings → Privacy to adjust.</value>
-  </data>
-  <data name="Migration_Webinterface_Removed_Title" xml:space="preserve">
-    <value>Hellion Chat 0.2.0</value>
-  </data>
-  <data name="Migration_Webinterface_Removed_Content" xml:space="preserve">
-    <value>The webinterface has been removed in this version because it could not be hardened to the privacy guarantees Hellion Chat makes by default. If you used it, please consult the README for context.</value>
-  </data>
   <data name="Wizard_Title" xml:space="preserve">
     <value>Hellion Chat — Welcome</value>
   </data>
@@ -276,9 +267,6 @@
   <data name="Export_Error" xml:space="preserve">
     <value>Export failed, see /xllog</value>
   </data>
-  <data name="Theme_Heading" xml:space="preserve">
-    <value>Appearance</value>
-  </data>
   <data name="Theme_Enabled_Name" xml:space="preserve">
     <value>Use the Hellion theme across all plugin windows</value>
   </data>
@@ -371,12 +359,6 @@
   </data>
 
   <!-- Hellion Chat — Auto-Tell-Tabs (runtime strings) -->
-  <data name="AutoTellTabs_Migration_Title" xml:space="preserve">
-    <value>Auto-Tell-Tabs</value>
-  </data>
-  <data name="AutoTellTabs_Migration_Content" xml:space="preserve">
-    <value>Auto-Tell-Tabs are enabled by default starting with version 0.4.0. You can disable or fine-tune them in the Chat tab.</value>
-  </data>
   <data name="AutoTellTabs_SectionHeader" xml:space="preserve">
     <value>Active Tells</value>
   </data>