index: create kind+timestamp index database

We don't build the index yet, but create the database like the others.

nostrdb.c

@@ -2208,6 +2208,11 @@ static int ndb_init_lmdb(const char *filename, struct ndb_lmdb *lmdb, size_t map
 	}
 	mdb_set_compare(txn, lmdb->dbs[NDB_DB_PROFILE_PK], ndb_tsid_compare);
 
+	if ((rc = mdb_dbi_open(txn, "note_kind", tsid_flags, &lmdb->dbs[NDB_DB_NOTE_KIND]))) {
+		fprintf(stderr, "mdb_dbi_open id failed: %s\n", mdb_strerror(rc));
+		return 0;
+	}
+	mdb_set_compare(txn, lmdb->dbs[NDB_DB_NOTE_KIND], ndb_u64_tsid_compare);
 
 	// Commit the transaction
 	if ((rc = mdb_txn_commit(txn))) {

nostrdb.h

@@ -37,10 +37,11 @@ enum ndb_dbs {
 	NDB_DB_META,
 	NDB_DB_PROFILE,
 	NDB_DB_NOTE_ID,
-	NDB_DB_PROFILE_PK,
+	NDB_DB_PROFILE_PK, // profile pk index
 	NDB_DB_NDB_META,
 	NDB_DB_PROFILE_SEARCH,
 	NDB_DB_PROFILE_LAST_FETCH,
+	NDB_DB_NOTE_KIND, // note kind index
 	NDB_DBS,
 };
 
@@ -525,6 +526,8 @@ ndb_db_name(enum ndb_dbs db)
 			return "profile_search";
 		case NDB_DB_PROFILE_LAST_FETCH:
 			return "profile_last_fetch";
+		case NDB_DB_NOTE_KIND:
+			return "note_kind_index";
 		case NDB_DBS:
 			return "count";
 	}