feat: add craft-goal session starter and command

Adds /craft-goal autocomplete and chat handling for starting a Goal crafting session.
Introduces new Magic Prompts content and localized labels/descriptions for Goal crafting.
Migrates desktop draft starters to include Craft a Goal once and persists the migration marker.

packages/ui/src/lib/i18n/messages/zh-TW.settings.ts

@@ -195,6 +195,9 @@
   'settings.magicPrompts.sidebar.item.sessionWorkspaceReview': '工作區審查',
   'settings.magicPrompts.sidebar.item.sessionExplore': '程式碼庫導覽',
   'settings.magicPrompts.sidebar.item.sessionFeaturePlan': '功能規劃',
+  'settings.magicPrompts.sidebar.item.sessionCraftGoal': '建立 Goal',
+  'settings.magicPrompts.page.group.sessionCraftGoal.title': '建立 Goal',
+  'settings.magicPrompts.page.group.sessionCraftGoal.description': '由 /craft-goal 斜線命令使用的提示詞：可見使用者訊息 + 隱藏說明。透過引導式探索將想法或任務轉化為清晰且有證據可驗證的 Goal。',
   'settings.magicPrompts.sidebar.item.sessionCatchUp': '快速回顧',
   'settings.magicPrompts.sidebar.item.sessionDebug': '除錯',
   'settings.magicPrompts.sidebar.item.sessionWeigh': '權衡方案',