v5.0.2 - MCP dependency fix

Dependency fix to prevent broken cm-mcp installs.

Fixed

• mcp package moved from [project.optional-dependencies.mcp] to core
  dependencies. The cm-mcp entry point is always registered, so a
  plain uv sync (without --extra mcp) would otherwise uninstall
  mcp/pydantic and break the MCP server with
  ModuleNotFoundError: No module named 'pydantic'.

Changed

• Install instructions in README and USER_GUIDE simplified: uv sync
  now installs everything needed for both CLI and MCP server. Only
  --extra embeddings / --extra all remain as opt-in extras.