test(e2e): mirror task id to index in TaskFactory

Multiple TaskFactory.create(1, {id: N, ...}, false) calls for the same
project were all defaulting to index=1 (from {increment} with count=1),
which collides on the newly added UNIQUE(project_id, index) constraint.
Mirror the numeric id override to index so each row stays unique and
matches the id == index convention used by raw seedTasks helpers.

Fixes the e2e playwright seed failures in subtask-duplicates, list/table
filter/search, kanban filter/search, and overview specs.

frontend/tests/factories/task.ts

@@ -15,7 +15,20 @@ export class TaskFactory extends Factory {
 			created_by_id: 1,
 			index: '{increment}',
 			created: now.toISOString(),
-			updated: now.toISOString()
+			updated: now.toISOString(),
 		}
 	}
+
+	// Mirror numeric `id` overrides onto `index` so sequential single-row
+	// creates don't collide on UNIQUE(project_id, index). Matches the
+	// id == index convention used by raw seedTasks helpers.
+	static async create(count = 1, override: Record<string, unknown> = {}, truncate = true) {
+		if (
+			typeof override.id === 'number' &&
+			!('index' in override)
+		) {
+			override = {...override, index: override.id}
+		}
+		return super.create(count, override, truncate)
+	}
 }