Rebuild the UI as an app shell: left sidebar, media gallery, structured events

Replaces the centered single-column of full-width cards with a proper application layout: a persistent left sidebar (Trees, and per-tree People/Sources/Media, with the tree name and sign-out) and a constrained content column. Marketing landing and auth pages are split out (own header/footer; centered auth with the logo).

Adds a Media gallery (upload + image thumbnails / file tiles, served via the backend content endpoint). Events are no longer free-text: a curated event-type list (+ custom) and a structured date (qualifier + day/month/year) that composes a proper genealogical date. Regenerated the OpenAPI client.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

frontend/app/trees/[id]/page.tsx

@@ -56,14 +56,7 @@ export default function TreeDetailPage() {
 
   return (
     <div className="space-y-6">
-      <div className="flex items-center justify-between">
-        <Link href="/trees" className="text-sm text-[var(--muted)] hover:underline">
-          ← All trees
-        </Link>
-        <Link href={`/trees/${treeId}/sources`} className="text-sm text-bronze hover:underline">
-          Sources →
-        </Link>
-      </div>
+      <h1 className="text-2xl font-semibold">People</h1>
 
       <Card>
         <CardHeader>