fix(web): make bot-link usable on public IP with HTTP

The "复制专属链接" button silently failed on public-IP HTTP deployments
because navigator.clipboard requires a secure context. Now the link is
always revealed in a modal with a read-only input (select-all on focus),
so users can copy manually even when clipboard APIs and execCommand both
fail. The dialog still tries to auto-copy when possible.

Also adds a publicUrl config option that overrides window.location.origin
for link generation (useful behind reverse proxies / with custom domains),
exposed via GET /api/config/public-url, and a trustProxy flag so Express
honors X-Forwarded-* when fronted by nginx/Caddy/Cloudflare.

https://claude.ai/code/session_019FSX3S3UUcKEYWanYmoqUv

src/index.ts

@@ -79,7 +79,10 @@ async function main() {
   await webServer.start();
 
   logger.info({ webPort: config.webPort }, "TSMusicBot started");
-  logger.info(`WebUI: http://localhost:${config.webPort}`);
+  const publicUrl = (config.publicUrl ?? "").trim().replace(/\/+$/, "");
+  logger.info(
+    `WebUI: ${publicUrl || `http://localhost:${config.webPort}`}`
+  );
 
   const shutdown = () => {
     logger.info("Shutting down...");