Build the GraphQL backend

[asgeija]

Build the custom Node + TypeScript GraphQL backend on port 3001. Search, sorting, filtering and pagination must run in the database so they cover the whole result set.

Sub-issues

• Scaffold the backend project #29
• Define the GraphQL schema #30
• Implement search, sort, filter and pagination resolvers #31

Done when

The frontend can query sightings with search, sorting, filtering and pagination.