docs: add design doc for decoupling scheduler and client from manager (#19)

• Introduce design for running Scheduler and Client without Manager
• Client selects local or remote dynconfig based on whether Manager is configured (None/nil)
• Local dynconfig loads from dynconfig.yaml (e.g., ConfigMap mount) and refreshes on a configurable interval (default 5s)
• Client discovers Schedulers via DNS headless service and builds a consistent hash ring from resolved IPs
• Scheduler disables Announcer when Manager config is absent
• Documents Kubernetes Manager-less deployment pattern using headless services and ConfigMaps