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/Plugin.cs

@@ -72,8 +72,11 @@ public sealed class Plugin : IDalamudPlugin
     // plugin start would launch two sweeps in parallel and the second one
     // would just re-do work the first one already finished. The lock guards
     // the flag — the flag check itself bails before we touch the database.
+    // Volatile because the ImGui thread reads the flag outside the lock to
+    // gate the manual button; without it the JIT may cache the value in a
+    // register and miss the background-thread update.
     internal readonly object RetentionSweepLock = new();
-    internal bool RetentionSweepRunning;
+    internal volatile bool RetentionSweepRunning;
 
     internal DateTime GameStarted { get; }