fix(crawler): translate socks5h:// → socks5:// for Chromium --proxy-server

Chromium doesn't know the socks5h scheme (curl/reqwest convention)
and bails navigations with ERR_NO_SUPPORTED_PROXIES. It does, however,
send destination hostnames over SOCKS5 by default, so stripping the
`h` is a pure scheme rename — remote-DNS behaviour is preserved.

reqwest keeps the user's original CRAWLER_PROXY string (`socks5h://...`
remains valid and meaningful for it).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/app.rs

@@ -140,7 +140,8 @@ async fn spawn_crawler_daemon(
     // authenticated without operator action.
     let mut launch_opts = cfg.browser.clone();
     if let Some(proxy) = &cfg.proxy {
-        launch_opts.extra_args.push(format!("--proxy-server={proxy}"));
+        let chromium_proxy = crate::crawler::url_utils::chromium_proxy_arg(proxy);
+        launch_opts.extra_args.push(format!("--proxy-server={chromium_proxy}"));
     }
     let on_launch = match (&cfg.phpsessid, &cfg.cookie_domain, &cfg.start_url) {
         (Some(sid), Some(domain), Some(start_url)) => {