feat(agent): add /status runtime command and Telegram entry

[bitifirefly]

Summary

• add /status command to agent loop for runtime snapshot (model, token usage, session size, subagent count, queue depth, uptime)
• track/reset last LLM usage stats each turn when provider usage is present/omitted
• include /status in /help command output
• register Telegram /status command and forward handler

Validation

• ruff check
• pytest -q tests/test_agent_loop_status_command.py tests/test_telegram_send_reply.py tests/test_agent_loop_safety.py tests/test_agent_loop_interim_retry.py
• pytest -q (full): 396 passed