Fix trigger value lost when local override is cleared while trigger remains active

[Copilot]

EvaluateTriggers() only fires when a condition property changes, so the re-apply path (wasActive && !HasLocalValue → shouldApplySetter = true) in Control.cs was never reached when a setter property was cleared — leaving the trigger value un-applied until the condition toggled.

Changes

DependencyObject — layered value store

• Added _localOverridesActiveTrigger: HashSet<DependencyProperty> to track when SetValue is called while a trigger is active
• Trigger value is now kept in _triggerValues when a local override is set (previously removed)
• GetValue precedence: PostTriggerLocal (_localOverridesActiveTrigger + _localValues) → Trigger (_triggerValues) → PreTriggerLocal → Inherited → Default
• ClearValue removes the override flag; the trigger value surfaces automatically on the next GetValue — no EvaluateTriggers() call needed
• ClearTriggerValue cleans up the override flag when the trigger deactivates

Control — remove flawed re-apply path

• Removed the wasActive && !target.HasLocalValue(...) re-apply block; the precedence model makes it unnecessary

Tests

• Added Trigger_ReExposesTriggerValue_AfterClearValueWhileActive regression test covering the full activate → SetValue → ClearValue → deactivate cycle

control.IsHovered = true;   // trigger active → TestValue == 42
control.TestValue = 999;    // local override
control.ClearValue(TestControl.TestValueProperty);
Assert.Equal(42, control.TestValue); // trigger value re-exposed without EvaluateTriggers()

control.IsHovered = false;
Assert.Equal(0, control.TestValue); // reverts to default on deactivate

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