feat(ui): scaffold vite + react 19 frontend

Replaces the CRA + React 16 + class-component frontend with the
shape from architecture/generic.md §4: vite + react + swc + ts,
served as static from nginx in prod, vite dev server in dev with
/api proxied to localhost:8080.

Layout:
  ui/
    package.json, vite.config.ts, tsconfig.{json,app,node}.json
    index.html
    src/
      main.tsx           — react root + react-query provider
      App.tsx            — header, filters, vertical timeline
      App.css            — dark backdrop, hot-pink links
      api/client.ts      — TS types mirroring moments-entities;
                            fetchEvents, fetchSources via /api/v1
      components/
        Filters.tsx      — source toggles, count slider, date range
        TimelineEntry.tsx — renders one TimelineItem with body
                             support for markdown, commits, links
      lib/icon.tsx       — TimelineIcon → react-bootstrap-icons map
                            + colour per icon

Stack: react 19, @tanstack/react-query 5, react-bootstrap 2 (on
bootstrap 5), react-vertical-timeline-component 3, rc-slider 11
(<Slider range /> replaces the removed v8 Range), react-markdown 9.

Dev proxy: /api/* → http://localhost:8080/* (rewrite strips /api).
Backend stays location-agnostic at /v1; ingress prefix is added
by nginx (and the dev proxy) so the same fetch shape works in
both environments.

Verified: tsc -b clean, vite build clean (417 KB js / 245 KB css
gzip 128 / 33), vite dev server serves the index. NOT verified
visually in a browser — that's a `pnpm run dev` away on roosta
once the api is up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/main.tsx

@@ -0,0 +1,21 @@
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
+import App from './App';
+
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 30_000,
+      retry: 1,
+    },
+  },
+});
+
+createRoot(document.getElementById('root')!).render(
+  <StrictMode>
+    <QueryClientProvider client={queryClient}>
+      <App />
+    </QueryClientProvider>
+  </StrictMode>,
+);