feat: add clipboard magic string for quick channel creation from token copy

When copying a token, users can now choose "Copy Connection String" which
encodes both the API key and server URL as a JSON clipboard payload
(type: newapi_channel_conn). When opening the channel creation form, the
clipboard is auto-detected and a banner offers to fill key + base_url,
eliminating repeated tab-switching when connecting to another new-api instance.

web/src/helpers/token.js

@@ -80,3 +80,41 @@ export function getServerAddress() {
 
   return serverAddress;
 }
+
+export const CHANNEL_CONN_CLIPBOARD_TYPE = 'newapi_channel_conn';
+
+/**
+ * @param {string} key - 完整的 API key（含 sk- 前缀）
+ * @param {string} url - 服务器地址
+ * @returns {string} JSON 格式的连接字符串
+ */
+export function encodeChannelConnectionString(key, url) {
+  return JSON.stringify({
+    _type: CHANNEL_CONN_CLIPBOARD_TYPE,
+    key,
+    url,
+  });
+}
+
+/**
+ * @param {string} text - 剪贴板文本
+ * @returns {{ key: string, url: string } | null}
+ */
+export function parseChannelConnectionString(text) {
+  if (!text || typeof text !== 'string') return null;
+  try {
+    const parsed = JSON.parse(text.trim());
+    if (
+      parsed &&
+      typeof parsed === 'object' &&
+      parsed._type === CHANNEL_CONN_CLIPBOARD_TYPE &&
+      typeof parsed.key === 'string' &&
+      typeof parsed.url === 'string'
+    ) {
+      return { key: parsed.key, url: parsed.url };
+    }
+  } catch {
+    // not valid JSON
+  }
+  return null;
+}