agent: scaffold Preact rewrite, Header + StatusChips first slice

Adds a new Preact/TSX build alongside the existing app.js (esbuild
entry `main.tsx` → dist/static/main.{js,css}, same jsx/tsconfig shape
swarm-ui already uses) and the first real page slice: Header +
StatusChips, composing the Badge/Dropdown components from the prior
commit's PR. Not wired into index.html yet — app.js keeps rendering
the live page untouched while this fills in component by component
(state polling, the live SSE stream, login flow, inbox/todos, term
input) in follow-up commits on this branch.

StatusChips folds the model/effort pickers and pause into the badge
row itself (each badge IS its own control), replacing the old
overflow-menu-only pickers — the concrete fix the design guide already
names this page as needing. Presentational only for now (props, not
live data) so it's reviewable against sample data before being wired
to /api/state.

Screenshot-verified against the real agent.css/theme.css/colors.css
(headless chromium, sample data) — renders correctly.

Builds + tsc --noEmit clean.

frontend/packages/agent/src/Root.tsx

@@ -0,0 +1,37 @@
+// <Root> — root of the Preact rewrite. Currently just `Header` +
+// `StatusChips` wired to local component state as a first slice (real
+// `/api/state` polling + the live SSE stream land in follow-up commits
+// on this same PR, per mara's "one pr != one commit" note on the
+// issue). Sample values below match the shapes in `types.ts`.
+import { useState } from 'preact/hooks';
+import { Header } from './components/Header.js';
+import { StatusChips } from './components/StatusChips.js';
+
+export function Root() {
+  const [model, setModel] = useState('sonnet');
+  const [effort, setEffort] = useState('high');
+  const [paused, setPaused] = useState(false);
+
+  return (
+    <Header label="IRIS" hiveLabel="constellation / pr1ma">
+      <StatusChips
+        aliveLabel="alive"
+        aliveTone="positive"
+        stateLabel="idle · 6m 1s"
+        stateTone="neutral"
+        stateTooltip="turn loop running, no claude invocation in flight"
+        model={model}
+        availableModels={['haiku', 'sonnet', 'opus']}
+        onSelectModel={setModel}
+        effort={effort}
+        availableEfforts={['low', 'medium', 'high', 'xhigh', 'max']}
+        onSelectEffort={setEffort}
+        ctxLabel="534k"
+        costLabel="$1.6M"
+        paused={paused}
+        onTogglePause={() => setPaused((p) => !p)}
+        lastTurnLabel="last turn 8.4s"
+      />
+    </Header>
+  );
+}