feat(widget): Widget 配置、loader 与右下角悬浮入口

生成可嵌入站点的 loader 与悬浮按钮，支持展开收起和移动端；附独立宿主测试页。

frontend/src/webclient/new-chat.ts

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2024-2026 ChatterMate
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Copy for the "New chat" control. Starting a new chat ends the current one for
+ * good, so both surfaces (chat header and the Ask AI bar) ask the same question in
+ * the same words, from here.
+ */
+export const NEW_CHAT_LABEL = '开始新会话'
+export const NEW_CHAT_CONFIRM_QUESTION = '开始新会话？当前会话将结束。'
+export const NEW_CHAT_CONFIRM_ACTION = '开始新会话'
+export const NEW_CHAT_CANCEL_ACTION = '取消'
+export const NEW_CHAT_FAILED_TEXT = "无法开始新会话，请重试。"
+
+/** How long the confirmation stays up before it gives up on being answered. */
+export const NEW_CHAT_CONFIRM_TIMEOUT_MS = 15000