Multi-skill module

Read this when the user asks what a module is made of, or has several skills that belong together.

A module is a record folder, bmod-<code>/, beside the skills it ships, plus a small bmod.toml in each member. The record holds: a SKILL.md that only says "never invoke this, ask bmad setup <code>"; bmod.toml with the code, version, update source, the member list, required and recommended skills, configuration questions and install messages; help/help.md, read by the bmad help agent, with optional help/<topic>.md files for depth; roster.toml when a member is an agent, so bmad and party mode know who is available; retired.toml once a skill has been renamed or removed, so setup can clean up. Each member's bmod.toml names the record and the source, and lists what that skill alone requires.

Members carry the module's code as a prefix (acme-release-notes, agents acme-agent-scout); bmad- names belong to modules shipped by the bmad-code-org (help/naming.md). Configuration is asked once, in the record, and every member reads the answer the same way. A skill belongs to one module; one it uses from another module is a dependency, not a member.

Smithy reaches this shape when the read-back names two or more skills, when one skill joins a record that exists (help/how-to-add-to-module.md), or through package mode for skills already written.