feat(cli): add completion for check require values

[leodido]

Summary

• register dynamic value completion for check --require
• support case-insensitive filtering, comma-separated values, and duplicate suppression
• add unit tests for completion helper behavior
• add BATS coverage for __complete check --require suggestions

Commits

• feat(cli): add require flag value completion
• test(cli): cover require completion behavior

Validation

• go test ./...
• manual: ./bin/kfeatures __complete check --require "BPF-SYSCALL,tr"