fix(libraries): declare DiagramLayout, IdentityMetadata, MigrationMetadata and SysMLValidation as library package

[devin-ai-integration]

Summary

Four libraries were declared standard library package. That keyword is reserved for the OMG standard library, and the pinned pilot validator warns on it (User library packages should not be marked as standard). They are non-normative extensions, so line 1 of each now reads:

-standard library package DiagramLayout {
+library package DiagramLayout {

The same change applies to IdentityMetadata, MigrationMetadata and SysMLValidation. No other library bytes change, and the change is identical to the one proposed in Open-MBEE/OpenSysML#882.

• validation/allowed-warnings.txt is now empty, so CI requires 0 errors and 0 warnings. The ratchet is unchanged: an allow-list entry the validator no longer emits still fails the gate.
• The README's Validation section and the validator's closing message no longer say "allow-listed".
• engine-contract.json is unchanged. Package names and members are the same, so this is not a contract change.

Local results:

• ./scripts/validate-libraries.sh prints Validation clean: 0 errors, 0 warning(s).
• check-engine-contract.sh passes.
• The .kpar build passes (16 units).

Merge with a merge commit. Open-MBEE/OpenSysML#881 pins this branch's head while both PRs are open. After this merges, I'll move #881's pin to the merge commit on main.

Link to Devin session: https://nasa-jpl-demo.devinenterprise.com/sessions/bf0cf4d7769a49a8adfee6bfd87860f3
Open in Devin Desktop: https://nasa-jpl-demo.devinenterprise.com/desktop/session/bf0cf4d7769a49a8adfee6bfd87860f3?variant=devin
Requested by: @HuiJun

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.