feat(ui): 添加全局Snackbar组件并替换局部实现

将原本分散在各组件的Snackbar功能统一为全局组件，通过Pinia store管理状态
移除CreateTemplateScreen中的局部Snackbar实现，改用全局组件
添加Snackbar store提供多种消息类型方法(success/error/warning/info)

src/renderer/store/snackbar.ts

@@ -0,0 +1,48 @@
+import { defineStore } from 'pinia'
+import { ref } from 'vue'
+
+export interface SnackbarAction {
+  text: string
+  color?: string
+  handler?: () => void
+}
+
+export const useSnackbarStore = defineStore('snackbar', () => {
+  const isVisible = ref(false)
+  const message = ref('')
+  const color = ref('info')
+  const timeout = ref(3000)
+  const actions = ref<SnackbarAction[]>([])
+
+  const show = (msg: string, clr = 'info', tout = 3000, actionList: SnackbarAction[] = []) => {
+    message.value = msg
+    color.value = clr
+    timeout.value = tout
+    actions.value = actionList
+    isVisible.value = true
+  }
+
+  const success = (msg: string, tout = 3000) => show(msg, 'success', tout)
+  const error = (msg: string, tout = 3000) => show(msg, 'error', tout)
+  const warning = (msg: string, tout = 3000) => show(msg, 'warning', tout)
+  const info = (msg: string, tout = 3000) => show(msg, 'info', tout)
+
+  const hide = () => {
+    isVisible.value = false
+    actions.value = []
+  }
+
+  return {
+    isVisible,
+    message,
+    color,
+    timeout,
+    actions,
+    show,
+    success,
+    error,
+    warning,
+    info,
+    hide
+  }
+})