Phase 0: project scaffold

- Go module + chi server with embedded SPA serving and /api/health
- internal/config env loader (local-dev defaults; auth/copyleaks deferred)
- React 19 + Vite 6 + Tailwind v4 frontend with full Petal design tokens
- Frontend embedded into the binary via web/embed.go (go:embed all:dist)
- README dev workflow, .env.example, BUILD_PLAN progress tracker
- Verified end-to-end: binary serves health, embedded SPA, and SPA fallback

web/src/App.tsx

@@ -0,0 +1,46 @@
+import { useEffect, useState } from 'react'
+
+// Phase 0 placeholder: proves the stack end-to-end — React + Tailwind v4 tokens
+// rendering, and the Go backend reachable via the /api proxy. Real UI lands in
+// later phases (DocList, Editor, StatusBar).
+export default function App() {
+  const [api, setApi] = useState<'checking' | 'ok' | 'down'>('checking')
+
+  useEffect(() => {
+    fetch('/api/health')
+      .then((r) => setApi(r.ok ? 'ok' : 'down'))
+      .catch(() => setApi('down'))
+  }, [])
+
+  return (
+    <div className="flex h-full flex-col items-center justify-center gap-6 px-6 text-center">
+      <div
+        className="flex flex-col items-center gap-3 bg-surface px-12 py-10"
+        style={{ borderRadius: 'var(--radius-card)', boxShadow: 'var(--shadow-soft)' }}
+      >
+        <span className="text-5xl">🌸</span>
+        <h1 className="text-3xl font-extrabold text-plum">Petal</h1>
+        <p className="max-w-xs text-muted" style={{ fontFamily: 'var(--font-body)' }}>
+          A cozy place to write.
+        </p>
+        <span
+          className="mt-2 inline-flex items-center gap-2 px-4 py-1.5 text-sm font-semibold"
+          style={{ borderRadius: 'var(--radius-pill)', background: 'var(--color-surface-alt)' }}
+        >
+          <span
+            className="inline-block h-2 w-2 rounded-full"
+            style={{
+              background:
+                api === 'ok'
+                  ? 'var(--color-success)'
+                  : api === 'down'
+                    ? 'var(--color-accent)'
+                    : 'var(--color-muted)',
+            }}
+          />
+          {api === 'checking' ? 'Checking backend…' : api === 'ok' ? 'Backend connected' : 'Backend offline'}
+        </span>
+      </div>
+    </div>
+  )
+}