refactor(server): type captureTally accumulators as PieceTally

Tighten the local byYou/byOpponent accumulators from the wider
Record<string, number> to PieceTally, matching the return type's fields
and preventing silent invalid-key writes.

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

packages/server/src/captures.ts

@@ -1,4 +1,4 @@
-import type { CaptureTally, Color } from '@blind-chess/shared';
+import type { CaptureTally, Color, PieceTally } from '@blind-chess/shared';
 import type { Game } from './state.js';
 
 /**
@@ -8,8 +8,8 @@ import type { Game } from './state.js';
  * no live board state, no opponent positions.
  */
 export function captureTally(game: Game, viewer: Color): CaptureTally {
-  const byYou: Record<string, number> = {};
-  const byOpponent: Record<string, number> = {};
+  const byYou: PieceTally = {};
+  const byOpponent: PieceTally = {};
   for (const rec of game.moveHistory) {
     const captured = rec.capturedPieceType;
     if (!captured) continue;