[feat] extend database schema with new tables and indexes

database/main/creature_special_ability.sql

@@ -0,0 +1,14 @@
+create table creature_special_ability
+(
+    creature_id        INTEGER not null
+        references creature
+            on delete cascade,
+    special_ability_id INTEGER not null
+        references special_ability
+            on delete restrict,
+    primary key (creature_id, special_ability_id)
+);
+
+create index idx_creature_sa_sa
+    on creature_special_ability (special_ability_id);
+