fix: store filePath when loading tasks in aggregator

The aggregated tasks weren't storing the filePath property, which is
needed by the update/archive/delete handlers to find the actual task
file on disk.

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

Co-Authored-By: Claude <noreply@anthropic.com>

src/aggregator/index.ts

@@ -215,6 +215,7 @@ export class BacklogAggregator {
 									projectName: project.name,
 									projectColor: project.color,
 									projectPath: projectPath,
+									filePath: taskPath,
 								};
 								this.tasks.set(key, aggregatedTask);
 								hasChanges = true;
@@ -379,6 +380,7 @@ export class BacklogAggregator {
 					projectName: project.name,
 					projectColor: project.color,
 					projectPath: projectPath,
+					filePath: taskPath,
 				};
 				const key = `${projectPath}:${task.id}`;
 				this.tasks.set(key, aggregatedTask);