fix(health): Require Redis in production, optional in local

Redis health check now returns error status when not configured in
production/staging environments, but remains optional in local dev.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/routes/health.ts

@@ -138,14 +138,16 @@ async function getDbHealth(): Promise<DbHealth> {
 
 async function getRedisHealth(): Promise<RedisHealth> {
   const start = Date.now();
+  const isLocal = process.env.NODE_ENV === 'development' || process.env.NODE_ENV === 'local' || !process.env.NODE_ENV;
 
   // Check if Redis is configured
   if (!process.env.REDIS_URL && !process.env.REDIS_HOST) {
+    // Redis is optional in local dev, required in prod/staging
     return {
-      status: 'ok', // Redis is optional
+      status: isLocal ? 'ok' : 'error',
       connected: false,
       latency_ms: 0,
-      error: 'Redis not configured',
+      error: isLocal ? 'Redis not configured (optional in local)' : 'Redis not configured (required in production)',
     };
   }