agent: wire Header/StatusChips to real /api/state polling

- useAgentState hook: polls GET /api/state (4s interval for now — see
  its file comment for why this isn't yet the SSE-triggered + login-
  only-timer cadence the old page used; that lands with the live
  stream + term-input commit, which is when clobbering the operator's
  in-progress input actually becomes a risk).
- format.ts: fmtTokens/fmtAge, same output shapes as app.js's.
- modelEffort.ts: POST /api/model + /api/effort (same-origin, plain
  fetch).
- dashboardBase.ts + pauseAction.ts: pause/resume POST to the
  *dashboard's* origin via a real <form> submit, kept unchanged from
  app.js — a cross-origin fetch needs CORS headers hive-c0re doesn't
  send, a form submit sidesteps that same as it already did.
- Root.tsx: wires it all together, including app.js's "any non-online
  status forces the turn-state badge to offline" behavior.

Screenshot-verified against a mock GET /api/state (real fetch, not
hardcoded props) + the real agent.css/theme.css/colors.css.

Builds + tsc --noEmit clean.

frontend/packages/agent/src/lib/modelEffort.ts

@@ -0,0 +1,25 @@
+// POST `/api/model` / `/api/effort` — same-origin (this agent's own
+// backend), so a plain `fetch` is safe unlike pause/resume (see
+// pauseAction.ts). `redirect: 'manual'` + the broad "ok" check below is
+// ported from app.js unchanged — the endpoints don't actually redirect
+// today, but treating an opaque redirect as success costs nothing and
+// matches the existing contract exactly.
+async function post(path: string, field: string, value: string): Promise<{ ok: boolean; detail?: string }> {
+  try {
+    const resp = await fetch(path, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+      body: new URLSearchParams({ [field]: value }),
+      redirect: 'manual',
+    });
+    const ok = resp.ok || resp.type === 'opaqueredirect' || (resp.status >= 200 && resp.status < 400);
+    if (ok) return { ok: true };
+    const detail = await resp.text().catch(() => '');
+    return { ok: false, detail: `http ${resp.status}${detail ? ' — ' + detail : ''}` };
+  } catch (err) {
+    return { ok: false, detail: err instanceof Error ? err.message : String(err) };
+  }
+}
+
+export const postModel = (name: string) => post('api/model', 'model', name);
+export const postEffort = (level: string) => post('api/effort', 'effort', level);