新增: AI Chat @灵感提及(ChatInput mention idea组)

- ChatInput.vue: MentionItem type加idea + mentionItems加idea过滤(title/description projectsStore.ideas) + mentionGroups加idea组 + selectMention插入[灵感: title]
- i18n zh/en: mentionGroupIdea
灵感走store同步computed(同project/task模式 无IPC)

src/i18n/en/aiChat.ts

@@ -90,6 +90,7 @@ export default {
     mentionHint: "{'@'} to mention project/task",
     mentionGroupProject: 'Projects',
     mentionGroupTask: 'Tasks',
+    mentionGroupIdea: 'Ideas',
     mentionNoMatch: 'No matching entity',
     mentionEmpty: 'No project/task to mention',