feat: add playful attack plugin

[variablenix]

Summary

• add a curated Go-native attack plugin inspired by CloudBot's target-based fun commands
• support canonical !attack <style> <nick> plus aliases such as !slap, !hug, !flirt, !compliment, !gift, and !high5
• render action styles with CTCP ACTION and message styles as ordinary IRC replies
• validate nickname targets and protect outbound text from IRC control characters
• register and enable the plugin by default, with documentation and tests

Verification

• go test ./...
• go test -race ./...
• go vet ./...
• go mod verify
• git diff --check