feat: resolve observer project page round default and add selector

The observer full project page used to call getProjectDetail without
a round, getting cross-round contaminated stats. It now resolves a
default — the currently OPEN round the project is in, falling back
to the most recently CLOSED one — and renders a selector chip in
the score card whenever the project participated in more than one
candidate round. Initial selection respects the ?round= query param.

A new observer procedure (getProjectRoundsForObserver) returns the
project's open or closed rounds for the picker.

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

src/app/(observer)/observer/projects/[projectId]/page.tsx

@@ -6,10 +6,13 @@ export const dynamic = 'force-dynamic'
 
 export default async function ObserverProjectDetailPage({
   params,
+  searchParams,
 }: {
   params: Promise<{ projectId: string }>
+  searchParams: Promise<{ round?: string }>
 }) {
   const { projectId } = await params
+  const sp = await searchParams
 
-  return <ObserverProjectDetail projectId={projectId} />
+  return <ObserverProjectDetail projectId={projectId} initialRoundId={sp.round} />
 }