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/index.ts

@@ -1,4 +1,5 @@
 import { serve } from '@hono/node-server'
+import { logger } from './lib/logger.js'
 import { app } from './app.js'
 import { runMigrations } from './db/startup.js'
 import { seedMockBots, seedClassicBots } from './engine/mock.js'
@@ -11,10 +12,10 @@ if (process.env.NODE_ENV === 'production') {
   const walletVars = ['BOTFIGHTS_NWC_URL', 'BOTFIGHTS_WALLET_ENCRYPTION_KEY']
   const missing = walletVars.filter(k => !process.env[k])
   if (missing.length > 0) {
-    console.warn(`[botfights] WARNING: Missing env vars: ${missing.join(', ')} — wallet/payment features disabled`)
+    logger.warn('env', `Missing env vars: ${missing.join(', ')} — wallet/payment features disabled`)
   }
   if (!process.env.CORS_ORIGIN || process.env.CORS_ORIGIN === '*') {
-    console.warn('[botfights] WARNING: CORS_ORIGIN not set — allowing all origins')
+    logger.warn('env', 'CORS_ORIGIN not set — allowing all origins')
   }
 }
 
@@ -26,7 +27,7 @@ await seedClassicBots()
 const port = Number(process.env.PORT) || 9100
 
 serve({ fetch: app.fetch, port }, () => {
-  console.log(`[botfights] server listening on http://localhost:${port}`)
+  logger.info('server', `listening on http://localhost:${port}`)
 
   // Start background fight loop so the site always has fresh activity
   startBackgroundFights()
@@ -34,14 +35,14 @@ serve({ fetch: app.fetch, port }, () => {
 
 // Graceful shutdown — drain in-flight fights before exiting
 const shutdown = async (signal: string) => {
-  console.log(`[botfights] ${signal} received, shutting down...`)
+  logger.info('server', `${signal} received, shutting down...`)
   const active = getActiveFighterCount()
   if (active > 0) {
-    console.log(`[botfights] ${active} fighters still active, waiting 10s...`)
+    logger.info('server', `${active} fighters still active, waiting 10s...`)
   }
   await new Promise(r => setTimeout(r, active > 0 ? 10_000 : 500))
   clearAllPending()
-  console.log('[botfights] shutdown complete')
+  logger.info('server', 'shutdown complete')
   process.exit(0)
 }
 process.on('SIGTERM', () => shutdown('SIGTERM'))