fix(ui): release global lock around suspend-branch sleep in inp_readline

The normal path of inp_readline unlocks the global `lock` around
select(), giving worker threads (http_upload / http_download / ai_client
in src/tools and src/ai) a window to acquire it and update the UI.
The suspend branch (entered while an external editor is active) used to
g_usleep(100000) and return NULL while holding the lock, so the main
thread monopolised it for the whole editor session and every in-flight
transfer froze; on a long composition (the customer's main /editor use
case) this could be long enough for server-side timeouts to fire.

Mirror the normal-path unlock / sleep / lock pattern so the same window
exists during the editor session. Workers in the suspended state print
through wnoutrefresh paths only (no direct doupdate / refresh / wrefresh
in src outside core.c / inputwin.c, all of which are already guarded
against suspended writes), so opening the window introduces no new race.

src/ui/inputwin.c

@@ -182,7 +182,13 @@ inp_readline(void)
 {
     // UI is suspended
     if (is_suspended || isendwin()) {
+        // Mirror the normal-path unlock/sleep/lock so worker threads
+        // (http_upload / http_download / ai_client) can acquire `lock`
+        // during the editor session — otherwise the main thread holds
+        // it continuously and every in-flight transfer freezes.
+        pthread_mutex_unlock(&lock);
         g_usleep(100000); // 100ms
+        pthread_mutex_lock(&lock);
         return NULL;
     }