Add Slack bot support and improve CLAUDE.md

[wolfdancer]

Summary

• Slack bot: Full SlackBot implementation using slack-bolt with Socket Mode — handles app_mention events, thread replies, slash commands (/approve, /quit, /hello), and outie admin commands
• SlackBotConfig: Pydantic-validated config with string-based Slack IDs (U... users, C... channels), mirrors the existing Discord config structure with back-references
• Unified CLI: New innieme discord|slack [-c config] entry point plus dedicated innieme_slack_bot script; both added to pyproject.toml
• Example config: slack_config.example.yaml with Slack app setup instructions
• Dependencies: Added slack-bolt to requirements.in / requirements.txt
• CLAUDE.md: Rewrote to cover data flow, Pydantic back-reference wiring, thread tracking, embedding/vector store selection, and implementation caveats (placeholder summary, in-memory Chroma, etc.)

Test plan

• pytest tests/test_slack_bot.py and pytest tests/test_slack_bot_config.py pass
• pytest (full suite) passes
• Slack bot starts with a valid slack_config.yaml and responds to @mentions in configured channels
• Discord bot still starts and works with existing config.yaml
• innieme discord and innieme slack CLI commands resolve correctly

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