- once a day a background thread records the latest GitHub release and the notices for each version; the welcome screen shows them from that cache, so no run waits on the network
- the release notice names the upgrade command for how TradingAgents was installed
- TRADINGAGENTS_NO_UPDATE_CHECK=1 turns the check off; unattended and CI runs never make it
- notices are read from a new `notices` key, so earlier versions keep reading `announcements`
