Refresh FinOps hub upgrade procedure for multi-version FOCUS adoption

[flanakin]

Summary

Phase 0 of FOCUS 1.4 work (parent: #2120). Refreshes the canonical "add a new FOCUS version" procedure before any 1.3/1.4 schema work begins, so subsequent phases follow a consistent, version-agnostic playbook.

Changes

src/templates/finops-hub/docs/README.md

• New step 0: confirm Cost Management has shipped a matching FOCUS export schema; if not, ship hub support as preview.
• New steps 5-8: open-data metadata, conformance regen via Build-FocusConformance.ps1, plugin skill file updates (5 listed paths), changelog entry.
• New "Handling multiple FOCUS versions in one cycle" subsection covering GA + preview naming and unversioned-function aliasing.

docs-mslearn/toolkit/hubs/data-model.md

• Clarifies that the hub schema version mirrors the FOCUS spec version it natively ingests, with up-conversion handled by the unversioned functions.
• Documents the preview convention: hub support that ships ahead of spec ratification or Cost Management export availability is labeled preview; unversioned aliases stay pinned to the latest GA schema.

No FOCUS 1.3/1.4-specific content lands here — that's tracked in later phases.

Closes #2121

Test plan

• Render README.md and confirm new steps and subsection display correctly.
• Render data-model.md and confirm new paragraphs display correctly.
• Spot-check all relative links resolve.

[Copilot]

Pull request overview

Refreshes the FinOps hubs documentation playbook for adding new FOCUS versions, with explicit guidance for preview vs GA handling and a clearer explanation of how hub schema versions relate to FOCUS spec versions.

Changes:

• Expanded the “add a new FOCUS version” procedure with dependency checks, open-data metadata, conformance regeneration, plugin reference updates, and changelog guidance.
• Added guidance for handling two FOCUS versions in a single release cycle (GA + preview) and keeping unversioned functions pinned to latest GA.
• Clarified in user docs that hub schema versions mirror the FOCUS version they natively ingest, and documented the preview convention.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/templates/finops-hub/docs/README.md	Updates the canonical upgrade procedure and adds multi-version (GA + preview) guidance.
docs-mslearn/toolkit/hubs/data-model.md	Clarifies schema-version-to-FOCUS coupling and documents preview behavior for hub schemas.

[flanakin]

🤖 [AI][Claude Code] Additional change beyond Copilot review

While addressing the grammar fix on data-model.md:66, surfaced a broader concern: the original wording conflated two distinct preview triggers — FOCUS spec maturity (legit) and Cost Management export availability (not legit, since hubs has its own lifecycle and shouldn't be permanently gated by another team's roadmap).

Updated both data-model.md and the README's step 0 to decouple them:

• Preview = FOCUS spec is still working draft (not ratified).
• Cost Management export availability is now described as a separate operational concern. A hub schema can be GA before Cost Management ships an export — the hub will ingest the new format as soon as the export becomes available.

Phase 4 (IngestionSetup_v1_4.kql) and phase 5 (HubSetup_v1_4.kql) already correctly mark v1_4 as preview because FOCUS 1.4 is working draft, not because of any Cost Management gap, so no downstream PRs need adjusting.

[flanakin]

🤖 [AI][Claude Code] PR Update Summary

Addressed: 1 review thread + scope expansion

• ✅ Implemented: 1 (Copilot grammar fix on data-model.md:66)
• 💬 Scope change: Decoupled hub preview status from Cost Management export availability. Hubs preview = FOCUS spec is working draft; Cost Management lag is a separate operational concern documented in changelog, not a GA gate.