Fix: add WidgetDataRepository.isPendingCompletion predicate

Stream M's WidgetActionProcessorTest.kt references this predicate but
Stream J's initial repo only exposed mark/clear mutators. Trivial addition:
reads the pending-completion set and checks membership.

Unblocks :composeApp:testDebugUnitTest (now green across all streams).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

composeApp/src/androidMain/kotlin/com/tt/honeyDue/widget/WidgetDataRepository.kt

@@ -129,6 +129,10 @@ class WidgetDataRepository internal constructor(private val context: Context) {
         store.writePendingCompletionIds(current)
     }
 
+    /** Whether a task id is currently queued for optimistic completion. */
+    suspend fun isPendingCompletion(taskId: Long): Boolean =
+        taskId in store.readPendingCompletionIds()
+
     /**
      * Compute the three summary counters shown on the widget:
      *  - overdueCount    — tasks with `isOverdue == true`