refactor: trim over-engineering (ponytail-audit)

- ws → devDependencies (src uses type-only; runtime comes via @fastify/websocket)
- delete bot/index.ts barrel; import casual-brain/driver directly
- untrack tsconfig.tsbuildinfo (already gitignored)
- vanillaCandidates: push-loop → .map()

94 tests pass, build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/server/test/integration/ai-game-casual.test.ts

@@ -7,7 +7,8 @@ import {
 } from '../../src/games.js';
 import { attachSocket } from '../../src/ws.js';
 import { createGameSchema } from '../../src/validation.js';
-import { CasualBrain, BotDriver } from '../../src/bot/index.js';
+import { CasualBrain } from '../../src/bot/casual-brain.js';
+import { BotDriver } from '../../src/bot/driver.js';
 import type { ServerMessage } from '@blind-chess/shared';
 
 let app: ReturnType<typeof Fastify>;