feat(content): bake and read flat collision assets

Append strict collision/topology payloads to the existing prepared package so later physics cutover can drop parsed DAT graphs without adding a second mapping or changing traversal behavior. The full 2,232,170-key catalog is deterministic across worker counts, exact-byte aliased, corruption-isolated, and cancellation-safe.

tests/AcDream.Bake.Tests/ExactPayloadAliasCatalogTests.cs

@@ -0,0 +1,24 @@
+namespace AcDream.Bake.Tests;
+
+public sealed class ExactPayloadAliasCatalogTests
+{
+    [Fact]
+    public void AliasRequiresCompleteByteEquality()
+    {
+        var catalog = new ExactPayloadAliasCatalog();
+        byte[] primary = [1, 2, 3, 4, 5];
+        catalog.Add(0x1234UL, primary);
+
+        Assert.True(catalog.TryFind(
+            [1, 2, 3, 4, 5],
+            out ulong primaryKey));
+        Assert.Equal(0x1234UL, primaryKey);
+
+        Assert.False(catalog.TryFind(
+            [1, 2, 3, 4, 4],
+            out _));
+        Assert.False(catalog.TryFind(
+            [1, 2, 3, 4, 5, 0],
+            out _));
+    }
+}