fix: preserve karma nicknames and expand attacks

[variablenix]

Summary

• preserve the target nickname casing in Karma announcements while keeping storage case-insensitive
• document that <nickname> is replaced by the actual Karma target
• expand the Attack plugin to cover the CloudBot-style attack families and aliases, including !spank
• add optional-target commands and command coverage tests

Verification

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