Add first-run wizard with three privacy profiles

Fresh installs now open a setup window on first plugin load that
asks the user to pick one of three starting profiles. Existing
ChatTwo users keep skipping the wizard because the v6→v7 migration
sets Configuration.FirstRunCompleted = true on the same pass that
seeds the Privacy-First defaults — they already saw the migration
notification and can reopen the wizard from the Privacy tab if
they want to choose differently.

The three profiles map to concrete configuration sets:

  Privacy-First (recommended): own-conversation whitelist (30
  channels), retention enabled with the spec defaults (Tells 365
  days, own-conversation channels 90, fallback 30).

  Casual: Privacy-First plus public chat (Say/Shout/Yell, both
  emote types, Novice Network) with a 1-day retention window so
  RP players can scroll back the last scene without keeping
  third-party speech forever.

  Full History: filter off, retention off, GDPR warning shown
  inline. Behaves like upstream Chat 2.

The wizard window is non-modal but covers a wide layout (three
side-by-side cards) and closing it without picking anything is
treated as accepting whatever defaults are already in place. The
Privacy tab gains a "show wizard again" button at the top so the
choice is reversible.

ChatTwo/Configuration.cs

@@ -62,6 +62,10 @@ public class Configuration : IPluginConfiguration
     public Dictionary<ChatType, int> RetentionPerChannelDays = [];
     public DateTimeOffset RetentionLastRunAt = DateTimeOffset.MinValue;
 
+    // Hellion Chat first-run wizard — opens once on a fresh install. Existing
+    // ChatTwo users skip it because the v6→v7 migration sets the flag.
+    public bool FirstRunCompleted;
+
     public int GetRetentionDays(ChatType type)
     {
         if (RetentionPerChannelDays.TryGetValue(type, out var userOverride))
@@ -238,6 +242,8 @@ public class Configuration : IPluginConfiguration
         RetentionDefaultDays = other.RetentionDefaultDays;
         RetentionPerChannelDays = other.RetentionPerChannelDays.ToDictionary(p => p.Key, p => p.Value);
         RetentionLastRunAt = other.RetentionLastRunAt;
+
+        FirstRunCompleted = other.FirstRunCompleted;
     }
 }