docs(agents): rename agent-hierarchy.md to agent-roster.md

Per mara's #4879 review (89815): the system has no agent hierarchy,
just a flat set scoped by the capability store, so the filename no
longer matched. The file already read "Agent roster & privileges"
after the earlier facts pass; rename it to match, and update the
four inbound references (docs/README.md, coordinator.md, config.md,
agent-service.nix).

docs/README.md

@@ -31,7 +31,7 @@ declarations.
 - **What state survives destroy / purge / restart?** →
   [`agent-lifecycle/persistence.md`](agent-lifecycle/persistence.md).
 - **Who can do what to whom — the agent roster and privilege?** →
-  [`agent-lifecycle/agent-hierarchy.md`](agent-lifecycle/agent-hierarchy.md).
+  [`agent-lifecycle/agent-roster.md`](agent-lifecycle/agent-roster.md).
 - **How does claude get its prompt, and what tools does it have?** →
   [`turn-loop/`](turn-loop/README.md) — the loop, binary shape, turn
   outcomes; sub-pages: [`claude-invocation`](turn-loop/claude-invocation.md),

docs/scheduler/coordinator.md

@@ -578,4 +578,4 @@ which is almost never desired. Leave off on non-x86 hosts.
 - `docs/agent-lifecycle/approvals.md` — approval flow + scheduled prompts
 - `docs/agent-lifecycle/persistence.md` — SQLite schema, state-dir layout
 - `docs/process/conventions.md` — wire protocol, recipient sentinels
-- `docs/agent-lifecycle/agent-hierarchy.md` — the agent roster and privilege
+- `docs/agent-lifecycle/agent-roster.md` — the agent roster and privilege

docs/turn-loop/config.md

@@ -59,7 +59,7 @@ sudo rejection rather than silently succeeding — easier to audit.
 
 `services.hyperhive.agent.user.uid`, `services.hyperhive.agent.user.gid`, and
 `services.hyperhive.agent.user.name` are the companion options; see
-`docs/agent-lifecycle/agent-hierarchy.md` — "Harness systemd unit shape" for the full
+`docs/agent-lifecycle/agent-roster.md` — "Harness systemd unit shape" for the full
 `user.*` surface.
 
 ## Dashboard links