New `services.hyperhive.swarm.controller.links` option (listOf {label,
icon, url}, same shape as the per-agent hyperhive.dashboardLinks) plus
a new GET /api/links route serving it, same pattern as the existing
hives/GET /api/hives.
Rather than one central hardcoded list, each service's own module
contributes its own entry when actually enabled on the controller's
host: swarm-authelia.nix, hive-matrix.nix (gated on gui.enable too,
since / on that vhost only serves fluffychat then) and
hive-forge/default.nix (gated on behindGateway) each push one entry,
the same list-merge idiom services.hyperhive.gateway.localNames
already uses. swarm-ui.nix contributes a static entry for its own
same-origin swagger docs. Adding a future service's link is a nix-only
change to that service's own module.
Verified: cargo build/clippy/test -p swarm-controller clean, a
throwaway nixosSystem eval confirms all 4 entries merge correctly into
SWARM_CONTROLLER_LINKS, nix build .#swarm-controller succeeds.
ba3a9ed94f