Migrate to SQLite3

We'll keep the door open for side-by-side support of Postgres in
the background, but due to SQLite's type system quirks we cannot
use the same DDL for both databases, so we would have to maintain
two sets of DDL (schema init and schema migration scripts) at once.

Interested future contributors can shoulder this maintenance burden
if they so choose.

schema/init/aime.sql

@@ -1,22 +1,14 @@
-create type "aime_region" as enum (
-    'JPN',
-    'HKG',
-    'SGP',
-    'KOR',
-    'USA'
-);
-
 create table "aime_shop" (
-    "id" bigint primary key not null,
+    "id" integer primary key not null,
     "ext_id" integer not null,
     "name" text not null,
-    "region" "aime_region" not null,
+    "region" text not null,
     constraint "aime_shop_uq" unique ("ext_id")
 );
 
 create table "aime_machine" (
-    "id" bigint primary key not null,
-    "shop_id" bigint not null
+    "id" integer primary key not null,
+    "shop_id" integer not null
             references "aime_shop"("id"),
     "pcb_id" text not null,
     "keychip_id" text not null,
@@ -25,15 +17,15 @@ create table "aime_machine" (
 );
 
 create table "aime_player" (
-    "id" bigint primary key not null,
+    "id" integer primary key not null,
     "ext_id" integer not null,
     "register_time" timestamp not null,
     constraint "aime_player_uq" unique ("ext_id")
 );
 
 create table "aime_card" (
-    "id" bigint primary key not null,
-    "player_id" bigint not null
+    "id" integer primary key not null,
+    "player_id" integer not null
             references "aime_player"("id")
             on delete cascade,
     "nfc_id" text not null,