feat: connect venue catalog to GraphQL

[alekskjo]

What changed?

• added paginated venues(offset, limit) queries to the GraphQL API
• connected the frontend venue catalogue to /project2/api/graphql
• removed mock venue data as the source for lists, details, map and challenges
• mapped backend venue types, opening hours and nullable fields to the existing frontend model
• handled venues without ratings, descriptions or websites
• configured the local Vite proxy for the backend on port 3001
• added tests for GraphQL mapping, errors and pagination
• updated the backend and venue-model documentation

Verification

• backend typecheck passed
• all 57 backend tests passed
• backend build passed
• Prettier passed
• ESLint passed
• all 27 frontend tests passed
• frontend production build passed

Remaining deployment work

This PR implements the application integration, but does not install the persistent backend service on the VM.

After merge, we still need to:

• run the backend persistently on the T07 VM
• proxy /project2/api/graphql through Apache to 127.0.0.1:3001
• verify the complete deployed flow from frontend to GraphQL and PostgreSQL without a local tunnel
• update the second-delivery documentation with the verified live status

Closes #9
Part of #8

[ktnielse]

Looks good. Tests and type checks pass. One suggestion: toVenueType throws on unknown venue types, which would break the whole page. A fallback would be safer.