Polish: imperial, clear-bed, keyboard nudging, empty states (#18)

Co-authored-by: Steve Dudenhoeffer <[email protected]>

web/src/editor/EditorHint.tsx

@@ -0,0 +1,18 @@
+import type { ReactNode } from 'react'
+import { cn } from '@/lib/cn'
+
+/** A non-interactive hint overlaid on the canvas (empty-state guidance). */
+export function EditorHint({ position = 'center', children }: { position?: 'center' | 'top'; children: ReactNode }) {
+  return (
+    <div
+      className={cn(
+        'pointer-events-none absolute flex p-6 text-center',
+        position === 'top' ? 'inset-x-0 top-16 justify-center' : 'inset-0 items-center justify-center',
+      )}
+    >
+      <p className="max-w-xs rounded-lg bg-surface/85 px-4 py-3 text-sm text-muted shadow-sm backdrop-blur">
+        {children}
+      </p>
+    </div>
+  )
+}