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/package-lock.json

@@ -991,7 +991,11 @@
         "@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"
       }
     },
     "packages/dashboard": {