Align Yaml module source layout to PSModule domain-grouping standards

[MariusStorhaug]

Summary

PSModule/Yaml currently keeps src/functions/public/*.ps1 and src/functions/private/*.ps1 in flat directories. PSModule standards recommend domain-grouped public/private function folders and group documentation pages.

Why

During PR #47 release-prep audits, we confirmed:

• public commands are not grouped by domain folder,
• private helpers are not organized to mirror public domains,
• group markdown docs beside public groups are missing.

This is structural drift against PSModule/docs module layout guidance. The refactor is broad (touches many files) and is intentionally deferred out of PR #47 to keep the release merge reviewable.

Canon references

• PSModule/docs src/docs/Modules/Standards.md
  • "Group by domain"
  • "Mirror public and private domains"
  • "Group documentation pages with source"

Proposed scope

1. Reorganize src/functions/public/ into domain folders.
2. Reorganize src/functions/private/ to mirror those domains.
3. Add <Group>.md files beside each public domain group.
4. Update any build/discovery assumptions and tests impacted by path changes.

Acceptance criteria

• Public and private function paths follow domain grouping conventions.
• Group docs exist for each public function domain.
• Existing command behavior remains unchanged.
• Full test suite passes after reorganization.

Out of scope

• Functional YAML behavior changes.
• PR 🌟 [Major]: New PowerShell module v1.0.0 with complete YAML 1.2.2 command suite #47 release narrative/content changes beyond exception linkage.