fix(server/migrate): 000024 sqlite 重建 subscriptions 后补回 idx_subs_user_exp 索引 + 回归断言

000024 迁移重建 subscriptions 表(source CHECK 扩容)时未重新创建
idx_subs_user_exp(user_id, expires_at)索引,导致 SQLite(生产 pangolin1
实际驱动)上订阅按 user_id/expires_at 查询退化为全表扫描。up/down 均补回
CREATE INDEX,并在 TestSQLiteMigrateUpDown 里加断言防止再次静默丢失。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

server/internal/store/sqlite_migrate_test.go

@@ -50,6 +50,19 @@ func TestSQLiteMigrateUpDown(t *testing.T) {
 		}
 	}
 
+	// 2b. idx_subs_user_exp survives the 000024 subscriptions table rebuild
+	// (SQLite table-rebuild migrations silently drop indexes unless recreated;
+	// this guards against that regression — see 000024_invite_rewards.{up,down}.sql).
+	var idxCount int
+	if err := db.QueryRow(
+		`SELECT COUNT(*) FROM sqlite_master WHERE type='index' AND name='idx_subs_user_exp'`,
+	).Scan(&idxCount); err != nil {
+		t.Fatalf("query idx_subs_user_exp: %v", err)
+	}
+	if idxCount != 1 {
+		t.Errorf("idx_subs_user_exp count = %d, want 1 (index lost on subscriptions rebuild?)", idxCount)
+	}
+
 	// 3. Seed: 3 plans + directory_version singleton.
 	var plans int
 	if err := db.QueryRow(`SELECT COUNT(*) FROM plans`).Scan(&plans); err != nil {