Add security notes, validate spreadsheet URL, warn in framing template

Remove update_framing tool and sanitize error messages

Split README into separate Slack bot and MCP server setup guides

Update README to reference generic LLMs and MCP clients

Regenerate lockfile for litellm dependency

Switch from Anthropic SDK to litellm for multi-model support

Rewrite README for both Slack bot and MCP server usage

Fix README: update tool names and config docs

Initial open-source release