[Change] Core and modules docs alignment

[djm81]

Summary

Audit and align the full live documentation set for the post-modularization architecture.

Why

The docs still carry drift from the pre-modularized CLI. Some pages still imply a large flat command surface, marketplace guidance is split or duplicated, and module-specific command docs are not yet clearly separated from core runtime docs.

Scope

• audit all live first-party Markdown in README.md and docs/
• align command docs to lean core plus marketplace-installed grouped bundle commands
• consolidate marketplace/install/publish/trust/signing guidance
• update architecture, directory-structure, dependency, and module-development docs to reflect specfact-cli core vs specfact-cli-modules
• add explicit note that module-specific docs are temporarily hosted in core and will migrate to specfact-cli-modules
• update docs navigation and cross-links
• add lightweight docs parity validation where practical

OpenSpec

• Change ID: docs-01-core-modules-docs-alignment
• Repo: nold-ai/specfact-cli