refactor: standardize error handling with toError() helper

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

server/src/routes/bets.ts

@@ -1,4 +1,5 @@
 import { Hono } from 'hono'
+import { toError } from '../lib/utils.js'
 import { db, schema } from '../db/index.js'
 import { eq, desc } from 'drizzle-orm'
 import { calculateOdds } from '../engine/odds.js'
@@ -104,7 +105,7 @@ betsRouter.post('/place', rateLimit(60_000, 10), async (c) => {
       potentialPayout: bet.potentialPayout,
     })
   } catch (err: unknown) {
-    return c.json({ error: err instanceof Error ? err.message : String(err) }, 400)
+    return c.json({ error: toError(err).message }, 400)
   }
 })