chore: add task tool

[tankdonut]

Adds go-task/task (v3.51.1, MIT) — a task runner / build tool that aims to be simpler and easier to use than GNU Make.

task:
  download_url: {{repo_url}}/releases/download/v{{version}}/{{name}}_{{os}}_{{arch}}.tar.gz
  repo_url: https://github.com/go-task/task
  license: MIT
  version: 3.51.1
  sha256: da7e92f0ff961ef2aae7cfecbad8d1fd2a08d7b09ba968673adf7ff389b243b5

Note: upstream names the .tar.gz archives without the version (task_linux_amd64.tar.gz), so the template follows the no-version convention used by tflint/terragrunt rather than the versioned pattern used by flux.

Verified: schema validation, ruff lint/format, full test suite (154 passed).