feat(billing): add dual formulas, disable 10yuan gift, retry auto-renew

Turn off the low-balance 10 CNY signup bonus while keeping the 5 CNY
registration credit, split metering into independent formula A/B scopes,
and retry expired auto-renew subscriptions after recharge or hourly worker.

Co-authored-by: Cursor <cursoragent@cursor.com>

schema.sql

@@ -13,6 +13,7 @@ CREATE TABLE IF NOT EXISTS h5_users (
   workspace_root VARCHAR(512) NOT NULL,
   low_balance_gift_eligible TINYINT(1) NOT NULL DEFAULT 0,
   low_balance_gift_granted_at BIGINT NULL,
+  billing_formula ENUM('A','B') NOT NULL DEFAULT 'A',
   created_at BIGINT NOT NULL,
   updated_at BIGINT NOT NULL,
   UNIQUE KEY uq_h5_users_slug (slug),