test(dv-3): add 4-level roll-up + deep-leaf filter tests; return AsReadOnly; add caller-contract remark

Fix 1 (Important): RollUp_FourLevelDeepBadQuality_ReachesRoot — proves bad quality at a
4-segment-deep leaf propagates HasBadQuality up every ancestor to the root.

Fix 2 (Important): Filter_DeepLeafMatch_RetainsAllAncestorBranches — proves filtering on
a terminal segment of a 3-level path retains all ancestor branches.

Fix 3 (Minor): BuildAttributeTree now returns roots.AsReadOnly() so the returned
IReadOnlyList<DebugTreeNode> reference is not a mutable list.

Fix 4 (Minor): Added <remarks> XML doc to BuildAttributeTree noting the caller-contract
that at most one AttributeValueChanged per AttributeName should be passed.

All 18 DebugTreeBuilder tests pass.

tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/DebugTreeBuilderTests.cs

@@ -203,4 +203,33 @@ public class DebugTreeBuilderTests
         var tree = DebugTreeBuilder.BuildAttributeTree(Array.Empty<AttributeValueChanged>(), null);
         Assert.Empty(tree);
     }
+
+    [Fact]
+    public void RollUp_FourLevelDeepBadQuality_ReachesRoot()
+    {
+        var tree = DebugTreeBuilder.BuildAttributeTree(
+            new[] { Attr("A.B.C.D", quality: "Bad") }, null);
+
+        var a = Assert.Single(tree);
+        Assert.True(a.HasBadQuality);
+        var b = Assert.Single(a.Children);
+        Assert.True(b.HasBadQuality);
+        var c = Assert.Single(b.Children);
+        Assert.True(c.HasBadQuality);
+        var d = Assert.Single(c.Children);
+        Assert.True(d.HasBadQuality);
+    }
+
+    [Fact]
+    public void Filter_DeepLeafMatch_RetainsAllAncestorBranches()
+    {
+        var tree = DebugTreeBuilder.BuildAttributeTree(
+            new[] { Attr("Motor1.Compressor.Pump"), Attr("Motor1.Speed") }, "Pump");
+
+        var motor = Assert.Single(tree);
+        Assert.Equal("Motor1", motor.Key);
+        var compressor = Assert.Single(motor.Children);
+        Assert.Equal("Motor1.Compressor", compressor.Key);
+        Assert.Equal("Motor1.Compressor.Pump", Assert.Single(compressor.Children).Key);
+    }
 }