refactor(#1865): consolidate agent + manager socket servers into one

The per-agent and manager sockets ran two parallel dispatchers with
duplicated lifecycle handlers (agent-side topology-gated, manager-side
ungated) plus a manager-only handler set. Collapse to one parameterized
server in socket_server.rs:

- one serve() + dispatch(req, agent, privileged, coord); start() binds
  the per-agent sockets (privileged=false), start_manager() binds the
  manager socket (privileged=true).
- each lifecycle/config handler (start/restart/kill/update/init_config/
  apply_commit) merges its dual: the topology guard (require_child /
  require_new_child) runs only on the !privileged path; init_config
  records the requester as parent only when !privileged. restart keeps
  the orthogonal, capability-gated + audited infra-container branch.
- the agent-state queries (loose-ends / reminder count + rollup) branch
  on privileged: privileged keeps any-target + the "*" hive-wide sweep
  (query_agent_state-gated), non-privileged keeps the topology/cap gate.
- the privileged-only verbs (schedules / meta-inputs / get_logs) plus
  the submit/schedule/watchdog helpers move into socket_server; they are
  reached via dispatch_privileged_only(), which rejects the whole group
  on a non-privileged socket.
- delete manager_server.rs; repoint refs; merge the test modules.

No behavior change: the topology guard still applies on every
non-privileged lifecycle call, the privileged socket still acts on any
agent, and privileged-only verbs are still rejected on agent sockets.

hive-c0re/src/topology.rs

@@ -140,7 +140,7 @@ pub fn resolve_recipient_in(
 /// `candidate` upward; the walk terminates at root or on a cycle
 /// (cycle defence: bounded to 32 hops, more than any plausible
 /// hive depth). Used by the cancel-authorization check in
-/// `manager_server::handle_cancel_schedule` to enforce
+/// `socket_server::handle_cancel_schedule` to enforce
 /// "managers can cancel anything their subtree owns."
 #[must_use]
 pub fn is_descendant_of(candidate: &str, ancestor: &str) -> bool {