Display rank-up vote winner on the post-voting upkeep screen

The post-voting (deep_upkeep) screen now names who won the rank-up vote
and their new rank, instead of just "Voting complete!". Adds
Game.last_rank_up_player_id (+ migration), set when votes are tallied
and cleared when the next scene begins; falls back to a "no one ranked
up" message when there were no votes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/components/UpkeepPhase.svelte

@@ -13,6 +13,10 @@
 
     // Helpers
     $: hand = state.player.hand_cards ? JSON.parse(state.player.hand_cards) : [];
+    // Winner of the rank-up vote, surfaced on the post-voting (deep_upkeep) screen.
+    $: rankUpWinner = state.game.last_rank_up_player_id
+        ? state.players.find(p => p.id === state.game.last_rank_up_player_id)
+        : null;
 
     // A nominee must be another living, in-play Pi-Rat: not the voter, not a
     // previous-scene Deep, and not dead / awaiting-recruit (they'd reset to
@@ -202,7 +206,11 @@
 
             {#if state.game.phase === 'deep_upkeep'}
                 <div class="voted-confirmation-box glass-panel">
-                    <p class="success-text">✔️ Voting complete! Results tallied.</p>
+                    {#if rankUpWinner}
+                        <p class="success-text">🏆 {displayName(rankUpWinner)} won the vote and ranked up to Rank {rankUpWinner.rank}!</p>
+                    {:else}
+                        <p class="success-text">✔️ Voting complete! No one ranked up this time.</p>
+                    {/if}
                 </div>
             {:else if hasVoted}
                 <div class="voted-confirmation-box glass-panel">