Fix cloud mode: ERB secrets, Redis auth, and Redis URL

- secrets.rb: Process ERB tags in secrets.yml and use ||= to not
  overwrite existing ENV vars (was clobbering SERVER_MODE=cloud with
  literal ERB string, causing app to fall into 'application' mode
  and redirect to /en/activate)
- license.rb: Use ENV['REDIS_URL'] for all Redis.new calls instead
  of defaulting to localhost (infrastructure Redis requires auth)
- redis.yml: Use ERB to read REDIS_URL env var for production
- sidekiq.rb: Process ERB when loading redis.yml

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

config/redis.yml

@@ -10,4 +10,4 @@ test:
 
 production:
   <<: *default
-  url: redis://127.0.0.1:6379
+  url: <%= ENV.fetch('REDIS_URL', 'redis://127.0.0.1:6379') %>