docs: rewrite README to position K8sClaw as Kubernetes-native OpenClaw

- Add 'Why K8sClaw?' comparison table (12 dimensions vs OpenClaw)
- Expanded architecture diagram with memory system, schedules, data layer
- Document all 5 CRDs with Kubernetes analogies
- Add persistent memory and ClawSchedule sections
- Update TUI docs with all 7 views and slash commands
- Design decisions table maps each choice to K8s primitives
- Updated project structure with all components

Author: AlexsJones