Janik von Rotz fc09e848fd feat: enhance shellcheck integration and improve code quality across task files ...

- Added new prompt file `prompts/07_run-shellcheck-and-fix-issues.md` for shellcheck linting and fixing
- Updated `help()` function in `task`, `task.template`, and `README.md` to use `local grep_pattern` variable for improved readability and maintainability
- Updated `lint()` function in `task` to run `shellcheck` on both `task` and `task.template` files
- Added `export` statements for `BUILDX_PLATFORM`, `CONTAINER_REGISTRY`, `CONTAINER_TAG`, and `DOCKERFILE` variables in `task` script
- Added `# shellcheck disable=SC1090` comment before sourcing files in `task` and `task.template` to suppress shellcheck warnings
- Updated