fix(editor): Ctrl-Z aborts editor and returns to profanity

Replaces the SIGTSTP=SIG_IGN inheritance approach (was commit 8) with a
detect-and-abort design that matches user expectation: Ctrl-Z inside
the editor brings you back to profanity instead of leaving the session
suspended.

- src/tools/editor.c: SIGTSTP reset back to SIG_DFL in the child so
  vim's :stop / Ctrl-Z actually stop the editor (revert previous
  SIG_IGN inheritance).
- src/tools/editor.c: new editor_check_stopped() — non-reaping waitpid
  poll for WIFSTOPPED. Lets prof_run detect Ctrl-Z / :stop / gdb-attach
  on the editor child.
- src/tools/editor.c: editor_emergency_kill() now sends SIGCONT before
  SIGTERM so the abort works on a STOPPED child too.
- src/tools/editor.c: _editor_exit_cb handles WIFSIGNALED cleanly with
  "Editor session cancelled." instead of printing garbage via
  WEXITSTATUS on a signaled child.
- src/profanity.c: SIGTSTP / SIGCONT signal handlers set flags consumed
  by the main loop. Editor STOPPED -> editor_emergency_kill (returns to
  the chat with the pre-alt+c readline buffer intact). Plain Ctrl-Z
  with no editor -> mutt-style drop the process group to the shell.
  SIGCONT -> refresh curses with clearok + ui_resize. While editor is
  active, swallow suspend_requested (race: vim's kill(0,SIGTSTP) beats
  waitpid seeing STOPPED — next poll catches it).
- src/tools/editor.h: declare editor_check_stopped and editor_is_active.

Verbose comment blocks across the branch tightened to one to two lines.

src/ui/core.c

@@ -64,10 +64,8 @@ static Display* display;
 
 static void _ui_draw_term_title(void);
 
-// Skip drawing while an external editor is active (ui_suspended) or after the
-// screen has been closed (endwin). The flag is authoritative and does not rely
-// on isendwin() staying TRUE, which a stray doupdate() during the session could
-// otherwise clear.
+// 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)
 {

src/ui/inputwin.c

@@ -182,10 +182,8 @@ 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.
+        // Mirror the normal-path unlock so workers aren't starved
+        // for the whole editor session.
         pthread_mutex_unlock(&lock);
         g_usleep(100000); // 100ms
         pthread_mutex_lock(&lock);
@@ -322,8 +320,8 @@ inp_get_line(void)
     while (!line) {
         line = inp_readline();
         ui_update();
-        // Let GLib sources (notably the editor child watch) dispatch so
-        // ui_resume can run if the prompt was raised mid-editor-session.
+        // Let the editor child watch dispatch — otherwise a prompt raised
+        // mid-editor-session deadlocks here.
         while (g_main_context_iteration(NULL, FALSE))
             ;
     }
@@ -354,8 +352,8 @@ inp_get_password(void)
     while (!password) {
         password = inp_readline();
         ui_update();
-        // Let GLib sources (notably the editor child watch) dispatch so
-        // ui_resume can run if the prompt was raised mid-editor-session.
+        // Let the editor child watch dispatch — otherwise a prompt raised
+        // mid-editor-session deadlocks here.
         while (g_main_context_iteration(NULL, FALSE))
             ;
     }

src/ui/ui.h

@@ -43,9 +43,8 @@ void ui_load_colours(void);
 void ui_update(void);
 void ui_redraw(void);
 void ui_resize(void);
-// Centralised physical-paint primitive: flushes the virtual screen unless the
-// UI is suspended (external editor active) or the screen has been closed. Use
-// this instead of raw doupdate() in any path reachable while suspended.
+// doupdate() wrapper that skips when the UI is suspended. Use this instead
+// of raw doupdate() to avoid the per-site whitelist class of bug.
 void prof_doupdate(void);
 void ui_focus_win(ProfWin* window);
 void ui_sigwinch_handler(int sig);