Only task authors as well as project contributors or higher can edit task skills.

# Problem

Right now on project/tasks/task.hbs, the UI to remove and add task skills is accessible by anyone.

We should change this so that only users who are able to edit tasks can interact with this part of the UI.

## Subtasks

- [ ] Wrap the `skill-button` collection as well as the `skill-typeahead` UI with an `{{#if (can 'edit task' task)}}` block
- [ ] Put a `{{related-skills}} component into the `else` part of the block.
- [ ] Fix any broken tests
- [ ] Add an acceptance test to `acceptance/task-editing-test.js` along the lines of "skills cannot be assigned to/from a task if user is not able to".
- [ ] Possibly: Add properties to `tests/pages/project/tasks/task.js` to support the above acceptance test. Something like `rendersTaskSkillsList`, `rendersRelatedSkills`, `rendersSkillsTypeahead`, etc.

從 project/tasks/task.hbs 開始，檢查現有的 skill-button、skill-typeahead 和 related-skills 用法。查看 acceptance/task-editing-test.js 以及 tests/pages/project/tasks/task.js 中的任務頁面物件，然後執行相關的驗收測試。完成的標準是：未授權使用者無法指派或移除任務技能，而已授權使用者仍保留編輯 UI。

由索引模型根據 Issue 內容生成。