feat(server): 新增统一 logger 入口与 /health liveness 端点

- src/server/logger.ts 包一层 console.*，给后续 pino/otel 迁移留单点
- interceptors.ts 的 logError 改走 logger.error，业务侧禁止直接 console.*
- /health 返回 'ok'，纯 liveness（不查 DB），DB 挂时探活仍绿

src/server/api/interceptors.ts

@@ -1,13 +1,14 @@
 import { ORPCError, ValidationError } from '@orpc/server'
 import { z } from 'zod'
+import { logger } from '@/server/logger'
 
 export const logError = (error: unknown) => {
-  console.error(error)
+  logger.error(error)
 }
 
 export const handleValidationError = (error: unknown) => {
   if (error instanceof ORPCError && error.code === 'BAD_REQUEST' && error.cause instanceof ValidationError) {
-    // If you only use Zod you can safely cast to ZodIssue[] (per ORPC official docs)
+    // ORPC ValidationError.issues are Zod issues in this app.
     const zodError = new z.ZodError(error.cause.issues as z.core.$ZodIssue[])
 
     throw new ORPCError('INPUT_VALIDATION_FAILED', {