swarm-ui: bootstrap new swarm-level frontend (Preact + wouter + TS + JSX)

Project-bootstrap scope per the issue: static build as a nix pkg,
empty start page for now, functionality deferred until auth against
authelia is figured out. Stack (Preact + wouter + TypeScript + JSX)
matches the shell decision from the earlier framework-paths thread —
a real SPA shell with a router and deep links, distinct from the
per-hive dashboard's vanilla-JS + custom-element MPA.

- New npm workspace frontend/packages/swarm-ui: one route (/), a
  wouter Switch/Route shell, a 404 fallback. Reuses @hive/shared's
  colors.css/theme.css/base.css for visual consistency; no other
  shared JS (the vanilla-JS el()/dom.js helpers are superseded by
  Preact in this shell).
- nix/packages/swarm-ui.nix: its own buildNpmPackage derivation
  (scoped to just this workspace via an explicit buildPhase), not
  folded into nix/packages/frontend.nix's packages.default closure —
  same reasoning swarm-controller/swarmctl already use for staying out
  of daemonBins: a hive that doesn't run the swarm controller
  shouldn't carry swarm-ui bytes.
- npmDepsHash recomputed in both frontend.nix and swarm-ui.nix (same
  shared lockfile, new deps: preact, wouter-preact, typescript).
- Added swarm-ui to nix/checks.nix alongside frontend, for the same
  FOD-staleness reason plus being the only thing that actually builds
  it in CI (not in packages.default's closure like frontend is, so
  nix flake check wouldn't otherwise touch it).
- npm run typecheck (tsc --noEmit) is available locally; not yet wired
  into CI — esbuild transpiles TS without type-checking, so that's a
  real gap, left as a follow-up rather than growing this bootstrap PR
  with a new CI workflow step.

Verified: nix build .#swarm-ui and .#frontend both succeed; npm run
build (root, all workspaces) succeeds; tsc --noEmit clean;
scripts/check-issue-refs.sh clean.

frontend/packages/swarm-ui/build.mjs

@@ -0,0 +1,59 @@
+// esbuild build for @hive/swarm-ui (project-bootstrap scope). Output
+// layout (`dist/`):
+//
+//   dist/index.html              served at GET /
+//   dist/static/main.js          served at /static/main.js (ESM bundle,
+//                                 Preact + wouter-preact)
+//   dist/static/main.js.map      source map sibling
+//   dist/static/colors.css       served at /static/colors.css
+//   dist/static/theme.css        served at /static/theme.css
+//   dist/static/swarm-ui.css     served at /static/swarm-ui.css (@import
+//                                 resolved from @hive/shared)
+//
+// Not yet wired into any Rust binary's `ServeDir` — swarm-controller
+// only serves `/health` today (see swarm-controller/README.md); this
+// just makes `dist/` buildable so nix/packages/swarm-ui.nix has
+// something to package. `.tsx` → JS: esbuild transpiles TypeScript
+// natively (types stripped, not checked) — run `npm run typecheck`
+// (plain `tsc --noEmit`) separately for real type errors; not yet
+// wired into CI.
+
+import { build } from 'esbuild';
+import { mkdirSync, copyFileSync, rmSync } from 'node:fs';
+import { dirname, resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const here = dirname(fileURLToPath(import.meta.url));
+const src = (p) => resolve(here, 'src', p);
+const dist = (p) => resolve(here, 'dist', p);
+const staticDir = (p) => resolve(here, 'dist', 'static', p);
+
+rmSync(dist(''), { recursive: true, force: true });
+mkdirSync(staticDir(''), { recursive: true });
+
+await build({
+  entryPoints: [src('main.tsx')],
+  outfile: staticDir('main.js'),
+  bundle: true,
+  format: 'esm',
+  platform: 'browser',
+  target: ['es2022'],
+  sourcemap: true,
+  logLevel: 'info',
+  jsx: 'automatic',
+  jsxImportSource: 'preact',
+});
+
+for (const entry of ['colors.css', 'theme.css', 'swarm-ui.css']) {
+  await build({
+    entryPoints: [src(entry)],
+    outfile: staticDir(entry),
+    bundle: true,
+    loader: { '.css': 'css' },
+    logLevel: 'info',
+  });
+}
+
+copyFileSync(src('index.html'), dist('index.html'));
+
+console.log('swarm-ui build ok →', dist(''));