map the component-model docs onto the current Diataxis IA

[joshua-temple]

Problem / why

The component-model docs need a home in the current docs IA before any behavior issue
prescribes a doc path. The docs tree was restructured into a journey-first Diataxis layout
under docs/src/content/docs/, so any older pointer (for example the stale versioning.md
path, now reference/versioning.md) is presumed out of date. This item audits the current tree
and maps where component-model docs belong by Diataxis role, so downstream doc work lands in the
right place.

Scope

• Audit the current docs/src/content/docs/ tree (start, guides, reference, internals).
• Map component-model documentation onto Diataxis roles: tutorial, how-to, reference, and
  explanation.
• Working placement to confirm or revise:
  • Reference: reference/manifest.md for the components: schema, reference/versioning.md
    for per-component version lines and tag prefixes, reference/generated-workflows.md for
    per-component files, reference/cli.md for any CLI surface.
  • How-to: a component-focused guide under guides/, distinct from guides/multi-repo.md
    (which covers many repos, not many components in one repo).
  • Explanation: start/how-it-works.md and internals/architecture.md describe the
    component-major model as the native schema.
• Produce the page-by-page placement that the behavior milestones and the consolidation pass
  follow.

Acceptance criteria

• A confirmed placement of component-model docs by Diataxis role against the current tree.
• The V, P, and R in-PR doc updates and the document the component model #298 consolidation pass have a clear target for each
  topic.

Dependencies

Blocks #298. Part of the monorepo epic #279.

[joshua-temple]

Implemented and merged: the component-model docs are mapped onto the current journey-first Diataxis IA (guides/components.md, reference/manifest.md, reference/versioning.md, start/how-it-works.md). PR #531.