fix: resolve cross-level dependency bug in add-dependency command

- Fix isCircularDependency function to properly handle numeric task ID lookups
- Add robust comparison for both string and numeric task IDs
- Add comprehensive test cases for cross-level dependency scenarios
- Resolves issue where subtasks could not depend on top-level tasks

Fixes #542

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Ralph Khreish <Crunchyman-ralph@users.noreply.github.com>

scripts/modules/dependency-manager.js

@@ -396,8 +396,9 @@ function isCircularDependency(tasks, taskId, chain = []) {
 			task = parentTask.subtasks.find((st) => st.id === subtaskId);
 		}
 	} else {
-		// Regular task
-		task = tasks.find((t) => String(t.id) === taskIdStr);
+		// Regular task - handle both string and numeric task IDs
+		const taskIdNum = parseInt(taskIdStr, 10);
+		task = tasks.find((t) => t.id === taskIdNum || String(t.id) === taskIdStr);
 	}
 
 	if (!task) {