Visibility 5: an item can be aimed at when the observer's book holds it and it is still fitted and whole

IsRevealed is now the observer's book (Entity.HasReveal) plus the live filter
(still on its ship, not IsDestroyed). The tier ladder and
GameplaySettings.TargetArmorInfoThreshold are deleted, with the 19 fixture
initializers and the Settings.asset line. Fixtures that aim at an item record
its reveal through RecordReveal; Aetheria.Shared exposes internals to
Aetheria.Shared.Tests for that. Unbuilt and untested at this commit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Assets/Scripts/ServerShared/Entity.cs

@@ -952,6 +952,10 @@ public abstract class Entity
     public IEnumerable<Reveal> RevealsOf(Entity subject) =>
         _reveals.TryGetValue(subject, out var book) ? book.Values : Enumerable.Empty<Reveal>();
 
+    // Whether this observer's book for `subject` holds `item`: the book's membership, no live gear read.
+    internal bool HasReveal(Entity subject, EquippedItem item) =>
+        _reveals.TryGetValue(subject, out var book) && book.ContainsKey(item);
+
     // The one derivation of how much this observer holds of `subject`: see Contact.
     public Contact ContactOf(Entity subject)
     {