Make agent creation swarm-only and refuse a name placed on another hive

swarm-controller's POST /api/agents now refuses (409) a name the swarm
has already placed on a different hive: a non-Destroyed declaration in
that hive's wanted state, or a SetAgentWanted node still queued for it.
The same name on the same hive is that agent being re-created and goes
through. A wanted state that cannot be read refuses (503/500) instead of
reading as "placed nowhere". Creations are serialised from that read to
the graph insert so two concurrent creations of one name cannot both
pass.

Hive-level creation is removed: hivectl `agent create` / `request-create`,
HostRequest::Spawn / RequestSpawn, the dashboard POST /api/request-spawn
route, and ApprovalKind::Spawn with its approve/resolve arms and the
approval-carrying `templates::spawn`. The swarm path (deploy request or
wanted-state sweep -> queue_first_deploy -> templates::first_deploy) used
none of them. Old `spawn` approval rows are skipped by collect_lenient,
as `init_config` rows were in a3b672d1.

policy.rs's comment on agent_object_name stated swarm-wide name
uniqueness as a fact; it now says where it is enforced and what that
check cannot see.

Refs #4396

frontend/packages/dashboard/src/call.js

@@ -114,7 +114,7 @@ export function operatorInboxAppendFromEvent(ev) {
   onCountsChanged();
 }
 
-// ─── approvals — the operator config-change / spawn approval queue ────────
+// ─── approvals — the operator config-change approval queue ────────
 const APPROVAL_TAB_KEY = "hyperhive:approvals:tab";
 // Derived approval state — cold-loaded from /api/state, then mutated
 // live by `approval_added` / `approval_resolved` dashboard events.
@@ -244,24 +244,14 @@ export function renderApprovals() {
       el(
         "span",
         { class: "glyph" },
-        isMergePr ? "⇒" : isUpdateMeta ? "↻" : isSchedule ? "⏱" : "⊕",
+        isUpdateMeta ? "↻" : isSchedule ? "⏱" : "⇒",
       ),
       el("span", { class: "id" }, "#" + a.id),
       el("span", { class: "agent" }, a.agent),
       el(
         "span",
-        {
-          class:
-            "kind" +
-            (isMergePr || isUpdateMeta || isSchedule ? "" : " kind-spawn"),
-        },
-        isMergePr
-          ? "merge-pr"
-          : isUpdateMeta
-            ? "meta-update"
-            : isSchedule
-              ? "schedule"
-              : "spawn",
+        { class: "kind" },
+        isUpdateMeta ? "meta-update" : isSchedule ? "schedule" : "merge-pr",
       ),
     );
     if (isMergePr && a.sha_short) head.append(el("code", {}, a.sha_short));
@@ -431,13 +421,11 @@ function renderApprovalHistory(root, history) {
       el(
         "span",
         { class: "kind" },
-        a.kind === "merge_config_pr"
-          ? "merge-pr"
-          : a.kind === "update_meta_inputs"
-            ? "meta-update"
-            : a.kind === "schedule_prompt"
-              ? "schedule"
-              : "spawn",
+        a.kind === "update_meta_inputs"
+          ? "meta-update"
+          : a.kind === "schedule_prompt"
+            ? "schedule"
+            : "merge-pr",
       ),
       " ",
     );