A declared agent that never reported (e.g. its first deploy was lost) had no hive in the roster row, so the wanted merge skipped it and swarm-ui showed 'no declaration' with the state control disabled. GET /api/agents/status now takes such a row's hive from the one hive whose declaration places the agent, so the declared state shows and the control works on deploy.
no behaviour change: a pure move of items and tests into new modules, plus
visibility edits (pub(crate)) and path updates in sibling modules that named
crate-root items. same routes, same OpenAPI, 561 tests before and after.
why: #5470, new features stop landing in one 6.4k-line file by default.
files outside swarm-controller/src: docs/agent-lifecycle/agent-roster.md,
swarm-ui JobsPage.tsx and AgentsPage.tsx, nix/host-modules/swarm-controller.nix
and swarm-grafana.nix hold comments that named main.rs for items that moved.
