fix #12: simplify auth adapter, add verifications table

drizzle/0003_add_verifications_table.sql

@@ -0,0 +1,8 @@
+CREATE TABLE IF NOT EXISTS "verifications" (
+  "id" text PRIMARY KEY NOT NULL,
+  "identifier" text NOT NULL,
+  "value" text NOT NULL,
+  "expires_at" timestamp NOT NULL,
+  "created_at" timestamp with time zone DEFAULT now(),
+  "updated_at" timestamp with time zone DEFAULT now()
+);