feat(scale): implement scale auto with persistent rules

[wjgong001]

Implement the sh1pt scale auto sub-command with:

• Local JSON persistence (~/.sh1pt/auto-scale-rules.json)
• --min, --max, --target-cpu, --cooldown options
• --enable/--disable to toggle auto-scaling
• --show to display current rules
• Input validation (min>=1, max>=min, 1<=cpu<=100, cooldown>=10s)
• Also improved cost command: show pricing reference table when no fleet data
• Also improved status command: show auto-scaling rules status