chore: relocate backend into apps/api ahead of monorepo merge

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/config/redis.config.js

@@ -0,0 +1,25 @@
+// Returns a connected Redis/Valkey client, or null when CACHE_DRIVER=memory.
+// Consumers must check for null before using Redis-specific features.
+// Use case: when project is going to have LiveView in future.
+
+const useRedis = process.env.CACHE_DRIVER !== 'memory';
+
+if (!useRedis) {
+  console.log('ℹ️   Cache driver: memory (Redis skipped)');
+  module.exports = null;
+} else {
+  const { createClient } = require('redis');
+
+  const client = createClient({
+    url: process.env.REDIS_URL || 'redis://127.0.0.1:6379',
+  });
+
+  client.on('error', (err) => console.error('[Redis] Connection error:', err));
+
+  (async () => {
+    await client.connect();
+    console.log('✅  Redis connected.');
+  })();
+
+  module.exports = client;
+}