feat(postgres): add postgres backend support and migration docs

go-backend/internal/store/postgres/sql/data.sql

@@ -0,0 +1,18 @@
+INSERT INTO "user" (id, "user", pwd, role_id, exp_time, flow, in_flow, out_flow, flow_reset_time, num, created_time, updated_time, status)
+VALUES (1, 'admin_user', '3c85cdebade1c51cf64ca9f3c09d182d', 0, 2727251700000, 99999, 0, 0, 1, 99999, 1748914865000, 1754011744252, 1)
+ON CONFLICT DO NOTHING;
+
+INSERT INTO vite_config (id, name, value, time)
+VALUES (1, 'app_name', 'flux', 1755147963000)
+ON CONFLICT DO NOTHING;
+
+DO $$
+BEGIN
+    IF to_regclass('public.user_id_seq') IS NOT NULL THEN
+        PERFORM setval('user_id_seq', (SELECT COALESCE(MAX(id), 0) FROM "user"));
+    END IF;
+    IF to_regclass('public.vite_config_id_seq') IS NOT NULL THEN
+        PERFORM setval('vite_config_id_seq', (SELECT COALESCE(MAX(id), 0) FROM vite_config));
+    END IF;
+END
+$$;