Add breaking-changes knowledge domain and review leaf skill

[JesperSchulz]

Summary

Seeds a new breaking-changes knowledge domain (AL API stability) for BCQuality, mirroring the structure of the merged error-handling domain: each article is a <slug>.md with sibling <slug>.good.al / <slug>.bad.al samples, and a new leaf review skill is wired into al-code-review.

The six articles (microsoft/knowledge/breaking-changes/)

1. do-not-change-published-procedure-signatures — Once a procedure is publicly reachable, changing its signature (add/remove/reorder params, change types or return type, toggle var) breaks dependents. Add a new procedure/overload instead; naming a previously unnamed return value is the one safe in-place change.
2. deprecate-public-members-with-the-obsolete-lifecycle — Never delete a published procedure outright; mark it [Obsolete('reason','tag')], keep it through a deprecation window, then remove it.
3. obsolete-table-fields-instead-of-deleting-them — Deleting/renaming a published table field is breaking and risks data loss; use ObsoleteState = Pending → Removed with reason + tag.
4. do-not-modify-code-already-marked-obsolete — Members under [Obsolete] or #if not CLEANxx are scheduled for removal; build on the replacement, don't extend the obsolete member.
5. do-not-expose-sensitive-data-through-public-api — Don't widen access to expose tokens, credentials, or SecretText; keep secrets internal/local and expose only non-sensitive business data.
6. choose-access-modifiers-deliberately — Default to internal/local; make a member public only when you intend to support it as a stable contract.

New leaf skill + wiring

• Adds microsoft/skills/review/al-breaking-changes-review.md (5 H2 sections: Source, Relevance, Worklist, Action, Output; outputs: findings-report; source domain breaking-changes).
• Wires the leaf into al-code-review.md (frontmatter sub-skills, ## Source bullet, line-6 description) and bumps the README leaf-skill count seven→eight, appending breaking-changes to the domain list.

Origin / IP

Content is written from scratch as general AL best practice and verified against Microsoft Learn for version-sensitive facts (the [Obsolete] attribute applies to procedures while ObsoleteState applies to objects/fields; SecretText is v23+, so it is referenced only in prose to keep all samples valid for [all]). All articles are bc-version: [all]. Object IDs 50300–50329, unique names and IDs across the batch.

Validation

• python .github/scripts/validate_frontmatter.py → 0 errors, 0 warnings
• Test-KnowledgeIndex.ps1 → PASSED (166 articles, deterministic, full coverage)

Expected conflict

The parallel interfaces (#42) and events (#43) PRs edit the same al-code-review.md sub-skills list and README count lines, so a trivial wiring conflict is expected when they land. Resolution: keep ALL leaves, and set the README count = base count + number of new domains merged.

Part of #34.