feat: native Codex and Claude input routing with plugin commands

[Pigbibi]

Summary

• add durable Codex-native steer and next-turn queue routing with Telegram choices
• add Claude Code steer support and a durable AgentBot next-turn fallback queue
• expose agent-aware skills and plugin commands, mapping /plugins to Codex /plugins or Claude Code /plugin
• detect and relay Codex and Claude plugin/skills terminal browsers with Telegram controls
• preserve optional backend compatibility without changing AgentBackend.send_message

Verification

• uv run ruff check src/ tests/
• uv run pyright src/telegram_agent_bot/
• uv run pytest -q (809 passed, 28 pre-existing dependency warnings)
• isolated tmux smoke checks against Codex CLI 0.151.0 and Claude Code 2.1.207 plugin/skills UIs

[github-actions]

🤖 Codex PR Review

⚠️ Review skipped: The Codex review could not be completed.

No Codex service URL or API key configured. Set CODEX_AUDIT_SERVICE_URL, ANTHROPIC_API_KEY, or OPENAI_API_KEY.

Please ensure a human reviewer checks this PR before merging.