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  shared JS (the vanilla-JS el()/dom.js helpers are superseded by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/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "@hive/swarm-ui",
+  "version": "0.0.0",
+  "private": true,
+  "description": "Swarm-level operator UI shell (project-bootstrap scope). Preact + wouter + TypeScript + JSX for a real SPA shell with a router and deep links, distinct from the per-hive dashboard's vanilla-JS + custom-element MPA. Empty start page for now; functionality is out of scope until swarm-controller's authelia-backed auth lands. Bundled by esbuild into a static dist; served by swarm-controller once that wiring exists.",
+  "type": "module",
+  "scripts": {
+    "build": "node ./build.mjs",
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@hive/shared": "*",
+    "preact": "10.29.8",
+    "wouter-preact": "3.10.0"
+  },
+  "devDependencies": {
+    "typescript": "7.0.2"
+  }
+}