refactor(pairing): remove redundant CLI commands

CLI pairing commands (list/approve/deny/revoke) are fully replaceable by
`nanobot agent -m "/pairing ..."`, which routes through the same
CommandRouter and handle_pairing_command() backend. Removing them
cuts 86 lines of duplicate surface area without losing any functionality.

- Remove pairing_app and its 4 subcommands from cli/commands.py
- Update format_pairing_reply() to drop the "Via CLI" line

nanobot/pairing/store.py

@@ -187,8 +187,7 @@ def format_pairing_reply(code: str) -> str:
         "Hi there! This assistant only responds to approved users.\n\n"
         f"Your pairing code is: `{code}`\n\n"
         "To get access, ask the owner to approve this code:\n"
-        f"- In this chat: send `/pairing approve {code}`\n"
-        f"- Via CLI: run `nanobot pairing approve {code}`"
+        f"- In this chat: send `/pairing approve {code}`"
     )