fix(chat): ignore stale turn completions after reconnect (#4643)

## Summary

Reloading a browser chat mid-turn can replay a completion event for an
older input and close the active turn too early.

This persists the last browser-owned input sequence and reuses it on
reconnect, so older completion events are ignored. The sequence is
cleared after the matching boundary, and reconnect avoids the
settled-peek shortcut while that sequence is active.

The persisted field is optional, so sessions without it keep their
existing behavior.

## Testing

- `pnpm --dir packages/trigger-sdk run test ./src/v3/chat.test.ts
./test/chat-turn-correlation.test.ts --run` — 67 passed
- `pnpm --dir packages/trigger-sdk run test --run` — 32 files, 379 tests
passed
- `pnpm run build --filter @trigger.dev/sdk`
- `pnpm run format`
- `pnpm run lint`

## Changelog

Browser chats now keep the active turn open across page reloads when
older completion records are replayed.

## ✅ Checklist

- [x] I have followed every step in the [contributing
guide](https://github.com/triggerdotdev/trigger.dev/blob/main/CONTRIBUTING.md)
- [x] The PR title follows the convention.
- [x] I ran and tested the code works

💯

Co-authored-by: Matt Aitken <matt@mattaitken.com>