修复: 全栈审查 FR-C1~C5 五项正确性 bug

- FR-C1 formattedEvents 时间漂移:事件入数组固 _ts 时间戳(project.ts push + ProjectDetail 用 _ts)，computed 重算不再刷历史时间为当前时刻
- FR-C2 sentiment 三档统一:模板 >0/<0/===0 + sentimentClass 同源 + i18n neutral(zh/en)，原模板>0 与 class>=0 矛盾
- FR-C3 Settings timer 泄漏:onUnmounted 清全部三个(原仅 _concurrencyTimer)
- FR-C4 MIGRATION_VERSION 死常量:删(零代码引用,run() if 链自管版本)
- FR-C5 AiConversationDetail 缺 readonly:加 readonly?: boolean(后端 generating 时返回)
来源 fullstack-review §3(已核实);cargo/vue-tsc 0 err

src/views/Settings.vue

@@ -745,9 +745,11 @@ onMounted(() => {
   syncConcurrencyConfig()
 })
 
-// 组件卸载清 debounce timer,防 unmount 后旧 timer 仍 fire 发无效 IPC(timer 泄漏)
+// 组件卸载清全部 debounce timer,防 unmount 后旧 timer 仍 fire 写已销毁 reactive(timer 泄漏 FR-C3)
 onUnmounted(() => {
   if (_concurrencyTimer) clearTimeout(_concurrencyTimer)
+  if (_knowledgeSaveTimer) clearTimeout(_knowledgeSaveTimer)
+  if (_toastTimer) clearTimeout(_toastTimer)
 })
 </script>