feat: task trash, triage trash and retention settings for every area; admin can forbid keeping things for good

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/storage/done_cleanup_test.go

@@ -82,7 +82,7 @@ func TestPurgeExpiredDoneTasks(t *testing.T) {
 	benInAnnasList := doneTask(t, s, ben.ID, shared.ID, "in Annas Liste", "2026-11-01T08:00:00Z")
 	openTask, _ := s.CreateThoughtWithDetails(anna.ID, "offen", "normal", "manual", "", "", "todo", "")
 
-	deleted, err := s.PurgeExpiredDoneTasks(now)
+	deleted, err := s.PurgeExpiredDoneTasks(now, true)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -94,7 +94,7 @@ func TestPurgeExpiredDoneTasks(t *testing.T) {
 	}
 	// Edge: exactly at the limit nothing happens yet
 	edge := doneTask(t, s, anna.ID, "", "Grenze", "2026-11-15T00:30:00Z")
-	_, _ = s.PurgeExpiredDoneTasks(now)
+	_, _ = s.PurgeExpiredDoneTasks(now, true)
 	if !exists(s, edge) {
 		t.Fatal("a task completed exactly 30 days ago stays until the limit has passed")
 	}