fix(editor): prevent UI redraw conflicts during editor suspend/resume

Guard against re-entrant editor launches, abort editor on Ctrl-Z,
and centralize suspend-aware redraws through prof_doupdate() to prevent
terminal corruption when SIGTSTP is received while editor is active.

Removes SIGUSR1 editor escape in favor of standard pkill <editor> recovery.

src/ui/core.c

@@ -54,6 +54,7 @@
 
 static int inp_size;
 static gboolean perform_resize = FALSE;
+static gboolean ui_suspended = FALSE;
 static GTimer* ui_idle_time;
 static WINDOW* main_scr;
 
@@ -63,6 +64,14 @@ static Display* display;
 
 static void _ui_draw_term_title(void);
 
+// Fail-safe gate: authoritative flag (doesn't depend on isendwin staying
+// TRUE), plus the regular endwin check for shutdown.
+static gboolean
+_ui_redraw_suspended(void)
+{
+    return ui_suspended || isendwin();
+}
+
 static void
 _ui_close(void)
 {
@@ -120,8 +129,7 @@ ui_sigwinch_handler(int sig)
 void
 ui_update(void)
 {
-    // UI is suspended
-    if (isendwin()) {
+    if (_ui_redraw_suspended()) {
         return;
     }
 
@@ -138,7 +146,7 @@ ui_update(void)
     title_bar_update_virtual();
     status_bar_draw();
     inp_put_back();
-    doupdate();
+    prof_doupdate();
 
     if (perform_resize) {
         perform_resize = FALSE;
@@ -180,21 +188,49 @@ void
 ui_suspend(void)
 {
     inp_suspend();
+    // Flush before flipping the flag (prof_doupdate skips while suspended).
+    prof_doupdate();
+    ui_suspended = TRUE;
     endwin();
 }
 
 void
 ui_resume(void)
 {
+    ui_suspended = FALSE;
+    clearok(stdscr, TRUE); // ncurses can't see vim's screen clobber
     refresh();
     inp_resume();
 }
 
+void
+ui_beep(void)
+{
+    if (!isendwin()) {
+        beep();
+    }
+}
+
+void
+ui_flash(void)
+{
+    if (!isendwin()) {
+        flash();
+    }
+}
+
+void
+prof_doupdate(void)
+{
+    if (!_ui_redraw_suspended()) {
+        doupdate();
+    }
+}
+
 void
 ui_resize(void)
 {
-    // UI is suspended
-    if (isendwin()) {
+    if (_ui_redraw_suspended()) {
         return;
     }
 
@@ -216,8 +252,7 @@ ui_resize(void)
 void
 ui_redraw(void)
 {
-    // UI is suspended
-    if (isendwin()) {
+    if (_ui_redraw_suspended()) {
         return;
     }