fix #12: add accounts table for Better Auth credential storage

drizzle/0002_add_accounts_table.sql

@@ -0,0 +1,17 @@
+CREATE TABLE "accounts" (
+  "id" text PRIMARY KEY NOT NULL,
+  "user_id" text NOT NULL,
+  "account_id" text NOT NULL,
+  "provider_id" text NOT NULL,
+  "access_token" text,
+  "refresh_token" text,
+  "access_token_expires_at" timestamp,
+  "refresh_token_expires_at" timestamp,
+  "scope" text,
+  "id_token" text,
+  "password" text,
+  "created_at" timestamp with time zone DEFAULT now() NOT NULL,
+  "updated_at" timestamp with time zone DEFAULT now() NOT NULL
+);
+ALTER TABLE "accounts" ADD CONSTRAINT "accounts_user_id_users_id_fk" FOREIGN KEY ("user_id") REFERENCES "public"."users"("id") ON DELETE cascade ON UPDATE no action;
+CREATE INDEX "accounts_user_id_idx" ON "accounts" USING btree ("user_id");