fix(templates): override rows on a derived template are not second definitions in the collision check (ScadaBridge#119)

CollisionDetector counted a derived template's own override row (same name as a
parent member, IsInherited=false) as a second definition alongside the
parent's row, so AddAttribute/AddAlarm/AddScript for a fresh name failed with a
false "Naming collision" once any override existed. The inheritance walk now
keeps a (type, name) shadow set: a member defined at a nearer level of the
chain shadows the same member further up (effective member set, by name),
including overrides at mid levels. Real collisions (e.g. against a composed
module) still report.

Regression tests in TemplateEngine.Tests (detector + service, attribute/alarm/
script, mid-level override, positive control); 6 fail without the fix.
The #118 importer's additions-before-overrides ordering is now unnecessary but
harmless and was left in place.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/CollisionDetectorTests.cs

@@ -197,6 +197,62 @@ public class CollisionDetectorTests
         Assert.Contains(collisions, c => c.Contains("dup.Shared"));
     }
 
+    // ========================================================================
+    // ScadaBridge#119: an OVERRIDE row on a derived template (own, IsInherited=false,
+    // same name as a parent member) is not a second definition of the member.
+    // ========================================================================
+
+    private static (Template parent, Template derived) OverrideFixture()
+    {
+        var parent = new Template("Base") { Id = 1 };
+        parent.Attributes.Add(new TemplateAttribute("A") { Id = 10, TemplateId = 1, DataType = DataType.Float });
+        parent.Alarms.Add(new TemplateAlarm("Al") { Id = 11, TemplateId = 1, TriggerType = AlarmTriggerType.ValueMatch });
+        parent.Scripts.Add(new TemplateScript("Sc", "return 1;") { Id = 12, TemplateId = 1 });
+
+        var derived = new Template("Slot") { Id = 2, ParentTemplateId = 1 };
+        derived.Attributes.Add(new TemplateAttribute("A") { Id = 20, TemplateId = 2, DataType = DataType.Float, Value = "9" }); // override
+        derived.Alarms.Add(new TemplateAlarm("Al") { Id = 21, TemplateId = 2, TriggerType = AlarmTriggerType.ValueMatch });
+        derived.Scripts.Add(new TemplateScript("Sc", "return 2;") { Id = 22, TemplateId = 2 });
+        return (parent, derived);
+    }
+
+    /// <summary>Verifies that override rows of every member kind are not collisions.</summary>
+    [Fact]
+    public void DetectCollisions_OverrideRowsOnDerivedTemplate_NoFalseCollision()
+    {
+        var (parent, derived) = OverrideFixture();
+        derived.Attributes.Add(new TemplateAttribute("New") { TemplateId = 2, DataType = DataType.String });
+        Assert.Empty(CollisionDetector.DetectCollisions(derived, new List<Template> { parent, derived }));
+    }
+
+    /// <summary>Verifies that an override on a mid-level template does not collide with the grandparent.</summary>
+    [Fact]
+    public void DetectCollisions_OverrideAtMidLevel_NoFalseCollision()
+    {
+        var gp = new Template("Root") { Id = 1 };
+        gp.Attributes.Add(new TemplateAttribute("A") { Id = 10, TemplateId = 1, DataType = DataType.Float });
+        var mid = new Template("Mid") { Id = 2, ParentTemplateId = 1 };
+        mid.Attributes.Add(new TemplateAttribute("A") { Id = 20, TemplateId = 2, DataType = DataType.Float });
+        var leaf = new Template("Leaf") { Id = 3, ParentTemplateId = 2 };
+        leaf.Attributes.Add(new TemplateAttribute("A") { Id = 30, TemplateId = 3, DataType = DataType.Float, IsInherited = true });
+        Assert.Empty(CollisionDetector.DetectCollisions(leaf, new List<Template> { gp, mid, leaf }));
+    }
+
+    /// <summary>Positive control: a real collision on a template that also has overrides is still reported.</summary>
+    [Fact]
+    public void DetectCollisions_OverrideRowPresent_RealCollisionStillDetected()
+    {
+        var (parent, derived) = OverrideFixture();
+        var module = new Template("Module") { Id = 3 };
+        module.Attributes.Add(new TemplateAttribute("Shared") { Id = 30, TemplateId = 3, DataType = DataType.Float });
+        derived.Compositions.Add(new TemplateComposition("dup") { Id = 1, TemplateId = 2, ComposedTemplateId = 3 });
+        derived.Attributes.Add(new TemplateAttribute("dup.Shared") { TemplateId = 2, DataType = DataType.Float });
+
+        var c = CollisionDetector.DetectCollisions(derived, new List<Template> { parent, derived, module });
+        Assert.Single(c);
+        Assert.Contains("dup.Shared", c[0]);
+    }
+
     // ========================================================================
     // Repeated composition blindness. A template composed into TWO
     // different slots was added to the global visited-set on the first slot, so