refactor: structured logging across server

Create server/src/lib/logger.ts with info/warn/error methods that add
[botfights:tag] timestamps. Replace bare console.log/warn/error calls
in index.ts, seed.ts, routes/fights.ts, engine/queue.ts, engine/mock.ts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/routes/fights.ts

@@ -1,4 +1,5 @@
 import { Hono } from 'hono'
+import { logger } from '../lib/logger.js'
 import { streamSSE } from 'hono/streaming'
 import { db, schema } from '../db/index.js'
 import { eq, desc } from 'drizzle-orm'
@@ -175,8 +176,8 @@ fightsRouter.post('/mock/batch/:count', async (c) => {
   const capped = Math.min(count, 500)
 
   startFightLoop({ maxFights: capped, intervalMs: 500, matchmakingStyle: 'mixed' })
-    .then(() => console.log(`[botfights] batch of ${capped} fights completed`))
-    .catch(err => console.error('[botfights] batch error:', err))
+    .then(() => logger.info('fights', `batch of ${capped} fights completed`))
+    .catch(err => logger.error('fights', 'batch error', err))
 
   return c.json({ message: `Started batch of ${capped} fights in background.` })
 })