feat: auto-pause expired accounts

backend/migrations/030_add_account_expires_at.sql

@@ -0,0 +1,10 @@
+-- Add expires_at for account expiration configuration
+ALTER TABLE accounts ADD COLUMN IF NOT EXISTS expires_at timestamptz;
+-- Document expires_at meaning
+COMMENT ON COLUMN accounts.expires_at IS 'Account expiration time (NULL means no expiration).';
+-- Add auto_pause_on_expired for account expiration scheduling control
+ALTER TABLE accounts ADD COLUMN IF NOT EXISTS auto_pause_on_expired boolean NOT NULL DEFAULT true;
+-- Document auto_pause_on_expired meaning
+COMMENT ON COLUMN accounts.auto_pause_on_expired IS 'Auto pause scheduling when account expires.';
+-- Ensure existing accounts are enabled by default
+UPDATE accounts SET auto_pause_on_expired = true;