feat: bell_on_complete — terminal bell when agent finishes

Adds a simple config option to play the terminal bell (\a) when the
agent finishes a response. Useful for long-running tasks — switch to
another window and your terminal will ding when done.

Works over SSH since the bell character propagates through the
connection. Most terminal emulators can be configured to flash the
taskbar, play a sound, or show a visual indicator on bell.

Config (default: off):
  display:
    bell_on_complete: true

Closes #318

cli.py

@@ -1036,6 +1036,8 @@ class HermesCLI:
         self.tool_progress_mode = CLI_CONFIG["display"].get("tool_progress", "all")
         # resume_display: "full" (show history) | "minimal" (one-liner only)
         self.resume_display = CLI_CONFIG["display"].get("resume_display", "full")
+        # bell_on_complete: play terminal bell (\a) when agent finishes a response
+        self.bell_on_complete = CLI_CONFIG["display"].get("bell_on_complete", False)
         self.verbose = verbose if verbose is not None else (self.tool_progress_mode == "verbose")
         
         # Configuration - priority: CLI args > env vars > config file
@@ -3126,6 +3128,12 @@ class HermesCLI:
                 # nothing can interleave between the box borders.
                 _cprint(f"\n{top}\n{response}\n\n{bot}")
             
+            # Play terminal bell when agent finishes (if enabled).
+            # Works over SSH — the bell propagates to the user's terminal.
+            if self.bell_on_complete:
+                sys.stdout.write("\a")
+                sys.stdout.flush()
+            
             # Combine all interrupt messages (user may have typed multiple while waiting)
             # and re-queue as one prompt for process_loop
             if pending_message and hasattr(self, '_pending_input'):