Add `core go qa` command with subcommands:
- fmt: check/fix code formatting (gofmt)
- vet: run go vet
- lint: run golangci-lint
- test: run tests
- race: run tests with race detector
- vuln: check for vulnerabilities (govulncheck)
- sec: run security scanner (gosec)
- quick: fmt, vet, lint only
- full: all checks
Default (no subcommand) runs fmt, vet, lint, test.
All commands support --fix flag where applicable.
Also update Taskfile.yml to use core CLI commands throughout.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
