fix(cli): Ctrl+C clears input buffer before exiting

Previously, pressing Ctrl+C while text was typed in the input prompt
would immediately exit Hermes. Now follows standard shell behavior:

- Text in buffer → Ctrl+C clears the line (like bash)
- Empty buffer → Ctrl+C exits

This means accidentally hitting Ctrl+C while composing a message just
clears the input instead of killing the session. A second Ctrl+C on
the empty prompt still exits as expected.

cli.py

@@ -2490,8 +2490,13 @@ class HermesCLI:
                 print("\n⚡ Interrupting agent... (press Ctrl+C again to force exit)")
                 self.agent.interrupt()
             else:
-                self._should_exit = True
-                event.app.exit()
+                # If there's text in the input buffer, clear it (like bash).
+                # If the buffer is already empty, exit.
+                if event.app.current_buffer.text:
+                    event.app.current_buffer.reset()
+                else:
+                    self._should_exit = True
+                    event.app.exit()
         
         @kb.add('c-d')
         def handle_ctrl_d(event):