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

@@ -2489,6 +2489,11 @@ class HermesCLI:
                 self._last_ctrl_c_time = now
                 print("\n⚡ Interrupting agent... (press Ctrl+C again to force exit)")
                 self.agent.interrupt()
+            else:
+                # 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()