Show claim block height in the portal status panel

'held since block XXXXXX in orange/green' instead of just 'held by
orange' — the backend already returned claimed_at_block (routes/places.ts),
it just wasn't wired into the frontend Place type or the status display.

frontend/src/stores/game.ts

@@ -14,6 +14,7 @@ export interface Place {
   claim_team: Team | null;
   claimed_by_pubkey: string | null;
   claimed_at: number | null;
+  claimed_at_block: number | null;
 }
 
 export interface LinkRow {

frontend/src/views/MapView.vue

@@ -272,7 +272,7 @@ watch(linkSourceId, redraw);
             class="font-bold uppercase"
             :class="selectedPlace.claim_team === 'orange' ? 'text-orange-neon text-glow-orange' : 'text-green-neon text-glow-green'"
           >
-            held by {{ selectedPlace.claim_team }}
+            held since block {{ selectedPlace.claimed_at_block ?? '?' }} in {{ selectedPlace.claim_team }}
           </span>
         </p>