Add reward codes table

ddl/migrations/0181_reward_codes.sql

@@ -0,0 +1,20 @@
+begin;
+
+create table if not exists reward_codes (
+    code text not null primary key,
+    mint text not null,
+    reward_address text not null,
+    amount bigint not null,
+    created_at timestamp without time zone not null default current_timestamp
+);
+
+create index if not exists reward_codes_mint_idx on reward_codes using btree (mint);
+create index if not exists reward_codes_reward_address_idx on reward_codes using btree (reward_address);
+
+comment on table reward_codes is 'Stores reward codes for distributing coins';
+comment on column reward_codes.code is 'Unique code for redemption';
+comment on column reward_codes.mint is 'Coin mint address';
+comment on column reward_codes.reward_address is 'Address of the reward instance onchain';
+comment on column reward_codes.amount is 'Amount of coins to reward';
+
+commit;