feat: TUI rule builder with CRUD and config persistence

[Fraser-Isbester]

Summary

• Rule builder form accessible from the Rules tab via n (new), e (edit), d (delete) key bindings
• Full CRUD — create, edit, and delete rules entirely from the TUI
• Config persistence — rules are written atomically to ~/.config/tusk/config.yaml and survive restarts
• Hot-swap — engine updates at runtime via UpdateRules(), no restart needed. First rule bootstraps the engine if none exists
• CEL autocomplete — When field suggests resource variables and CEL builtins as you type, filtered by prefix
• Live validation — CEL expressions validated on every keystroke with green/red feedback
• Status bar and help panel updated with rule builder hints

Changed files

File	Change
internal/tui/views/rule_form.go	New — form with Name, Resource, When (CEL + autocomplete), Action, Cooldown, Enabled, Dry Run
internal/tui/app.go	CRUD methods, key bindings, engine lifecycle, status/help updates
internal/config/config.go	Save() for atomic YAML persistence
internal/tui/views/rules.go	SetEngine() for nil→initialized transition
internal/tui/views/violations.go	SetEngine() for nil→initialized transition
cmd/tusk/main.go	Pass *config.Config to NewApp

Test plan

• Navigate to Rules tab, press n — form appears
• Tab through fields, type a CEL expression — autocomplete suggestions appear
• Verify live validation (green "Expression valid" / red error)
• Save — rule appears in table, check ~/.config/tusk/config.yaml
• Press e — form pre-populated, modify, save
• Press d — confirmation, delete, verify removed from config
• Restart tusk — rules persist
• Start with zero rules — create first rule, engine bootstraps