Fix Captain discovery for legacy and shared branches

[sridharkalaibala]

Captain discovery returned no shop details for legacy branches whose Captain switch was unset, and for tills serving several branches. Match the existing Captain access defaults, return the enabled branch display names, and include the Internet address only when all enabled branches share it.

Validation: three focused API tests passed. The handler was also tested read-only against the local GSHCL branch data, then the approved local update was restarted and its live discovery endpoint returned the names and shared Internet address. No staff details or branch IDs are returned.

[github-actions]

Merged to develop. Anyone can test this - you do not need write access.

Try it at https://develop.posnic.io, or run it yourself:

git fetch origin develop && git checkout develop
npm install && npm --prefix api install
npm run dev   # then http://localhost:3000

When you have tested it, say what you did and what happened, and set
QA passed or QA failed. If you cannot set labels, just comment -
a maintainer will.

Reporting that something is broken is as useful as fixing it. It is
better found here than by a shopkeeper.