fix: catch up chat messages missed while the event stream was down

[raulriera]

While you sit in a chat, new messages from the other person sometimes stopped appearing. The live message connection can't replay anything it missed, so whenever it briefly dropped — a network blip, switching between Wi-Fi and cellular, or coming back from the background — every message that arrived during the gap was silently lost until you left and reopened the chat. The app now notices when the connection comes back and refetches the conversation list plus the open chat to fill in whatever it missed, while skipping that work on the very first connection so there's no wasted fetch on open.

Test plan

• Sit in a chat, briefly drop the network, then have the other person send a message — it appears once the connection recovers.
• Background the app while a chat is open, receive messages, then reopen the app — the missed messages are there.
• Open a chat normally and confirm the initial load isn't followed by a redundant refresh.
• Log out and back in within the same session — the chat list loads normally with no errors.