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/package.json

@@ -5,12 +5,17 @@
   "description": "hive-ag3nt per-container web UI. Bundled by esbuild into a static dist; served by the in-container Rust binary at runtime via tower_http::ServeDir. Per-agent additions are layered on top via the hyperhive.frontend.extraFiles nix option.",
   "type": "module",
   "scripts": {
-    "build": "node ./build.mjs"
+    "build": "node ./build.mjs",
+    "typecheck": "tsc --noEmit"
   },
   "dependencies": {
     "@hive/shared": "*",
     "chart.js": "4.5.1",
     "dompurify": "^3.2.4",
-    "marked": "18.0.6"
+    "marked": "18.0.6",
+    "preact": "10.29.8"
+  },
+  "devDependencies": {
+    "typescript": "7.0.2"
   }
 }