merge upstream/dev into feat/migrate-electric-to-zero

Resolve 8 conflicts:
- Accept upstream deletion of 3 composio_*_connector.py (unified Google connectors)
- Accept our deletion of ElectricProvider.tsx, use-connectors-electric.ts,
  use-messages-electric.ts (replaced by Zero equivalents)
- Keep both new deps in package.json (@rocicorp/zero + @slate-serializers/html)
- Regenerate pnpm-lock.yaml