swarm-ui: move create-agent page off /agents, rename to CreateAgentPage

mara: the route should reflect creating an agent, and stay separate
from a future agent list page. Renamed AgentsPage -> CreateAgentPage
(file, component, css classes) and moved the route from /agents to
/create-agent - flat, not /agents/new, since index.html's relative
asset links only resolve correctly one path segment deep (filed
separately as a real bug, not fixed here). Leaves the bare /agents
path free for a future roster page.

frontend/packages/swarm-ui/src/pages/CreateAgentPage.tsx

@@ -0,0 +1,105 @@
+// <CreateAgentPage> — minimal agent creation form, POSTs to
+// swarm-controller's `POST /api/agents`. That endpoint only queues a
+// `CreateIdentity` job and returns its node id — the identity isn't
+// guaranteed to exist yet when this page gets a response — so this
+// page shows the queued confirmation and links to the Jobs page to
+// watch it settle, rather than duplicating JobqGraph's per-node
+// polling here. Scope matches the originating issue exactly: name
+// field only, no forge/deploy options (those aren't wired server-side
+// yet either).
+//
+// Lives at `/create-agent`, not `/agents` — a future agent *roster*
+// (listing existing agents) is the natural owner of the bare `/agents`
+// path, and this creation form is a distinct action from that list,
+// not a variant of it. Flat, not `/agents/new`: `index.html`'s asset
+// links are relative (`static/main.js`), which only resolve correctly
+// one path segment deep — a real bug, filed separately rather than
+// fixed here, but reason enough to avoid a nested route today.
+//
+// First real form in this package — no shared form kit exists yet, so
+// the input/button styling below is scoped to `CreateAgentPage.css`
+// rather than promoted into `ui/`. Promote the day a second page needs
+// one, same "don't build ahead of a second caller" rule `Panel`'s own
+// comment states.
+import { useState } from 'preact/hooks';
+import { Link } from 'wouter-preact';
+import { Panel } from '../ui/panel/Panel.js';
+import './CreateAgentPage.css';
+
+interface CreateAgentResponse {
+  node_id: number;
+}
+
+type SubmitState =
+  | { status: 'idle' }
+  | { status: 'submitting' }
+  | { status: 'done'; nodeId: number }
+  | { status: 'error'; message: string };
+
+// Client-side mirror of `hive_types::Ident` (1-63 chars of `[a-z0-9-]`) —
+// a `pattern` hint only, not a substitute for the server's own
+// validation; a name this rejects would fail server-side anyway, so
+// catching it before a round-trip is a pure UX win, not a new gate.
+const NAME_PATTERN = '[a-z0-9-]{1,63}';
+
+export function CreateAgentPage() {
+  const [name, setName] = useState('');
+  const [result, setResult] = useState<SubmitState>({ status: 'idle' });
+
+  async function submit(e: Event) {
+    e.preventDefault();
+    setResult({ status: 'submitting' });
+    try {
+      const r = await fetch('/api/agents', {
+        method: 'POST',
+        headers: { 'content-type': 'application/json' },
+        body: JSON.stringify({ name }),
+      });
+      if (!r.ok) throw new Error((await r.text()) || `http ${r.status}`);
+      const data = (await r.json()) as CreateAgentResponse;
+      setResult({ status: 'done', nodeId: data.node_id });
+      setName('');
+    } catch (err) {
+      setResult({ status: 'error', message: String(err) });
+    }
+  }
+
+  return (
+    <Panel title="create agent">
+      <p class="create-agent-intro">
+        Create a new agent's swarm-level identity. This only queues the job — check{' '}
+        <Link href="/jobs">jobs</Link> to watch it settle.
+      </p>
+      <form class="create-agent-form" onSubmit={submit}>
+        <div class="create-agent-field">
+          <label class="create-agent-label" for="agent-name">
+            agent name
+          </label>
+          <input
+            id="agent-name"
+            class="create-agent-input"
+            type="text"
+            value={name}
+            pattern={NAME_PATTERN}
+            title="1-63 chars: lowercase letters, digits, hyphens"
+            required
+            onInput={(e) => setName(e.currentTarget.value)}
+          />
+        </div>
+        <button class="create-agent-submit" type="submit" disabled={result.status === 'submitting'}>
+          {result.status === 'submitting' ? 'creating…' : 'create'}
+        </button>
+      </form>
+      {result.status === 'done' && (
+        <p class="create-agent-result create-agent-result-ok">
+          queued as job node #{result.nodeId} — <Link href="/jobs">watch it in jobs</Link>
+        </p>
+      )}
+      {result.status === 'error' && (
+        <p class="create-agent-result create-agent-result-error">
+          failed to queue: {result.message}
+        </p>
+      )}
+    </Panel>
+  );
+}