Core-LB-G14: Add cloud shim boundary guard

[RicheyWorks]

Overall Classification: WARN
Campaign: Core LoadBalancer Reliability Contract Campaign
Goal: Core-LB-G14
Scope: docs/test-only cloud shim boundary audit

Summary:

• Documents the core LoadBalancer cloud shim boundary around initializeCloud(...), optional CloudManager access, and nullable compatibility.
• Adds a read-only documentation guard for cloud boundary wording, not-proven boundaries, credential-looking assignments, and overclaim exclusions.
• Does not start Core-LB-G15.

Tests added/updated:

• Added AgentCoreLoadBalancerCloudBoundaryDocumentationTest.
• Updated docs/agent/CORE_LOADBALANCER_FEATURE_CONTRACT.md.

Verification:

• mvn test -Dtest=AgentCoreLoadBalancerCloudBoundaryDocumentationTest passed: 4 tests, 0 failures, 0 errors, 0 skipped.
• mvn test -Dtest=AgentCoreLoadBalancerCloudBoundaryDocumentationTest,AgentCoreLoadBalancerFeatureContractDocumentationTest,AgentCoreLoadBalancerReviewerEvidenceMapDocumentationTest,AgentCoreLoadBalancerEvidenceConsolidationDocumentationTest passed: 20 tests, 0 failures, 0 errors, 0 skipped.
• mvn -q test passed.
• mvn -q -DskipTests package passed.
• mvn -B package passed: 2,552 tests, 0 failures, 0 errors, 0 skipped.
• git diff --check passed.
• git diff --cached --check passed.
• git diff --check origin/main...HEAD passed.
• .\scripts\smoke\enterprise-lab-workflow.ps1 -Package passed.

Main-green prerequisite:

• Core-LB-G13 merge commit 28ef12b main CI and CodeQL were observed completed success before opening this PR.

Safety:

• No production code changed.
• No Maven config changed.
• No CI/workflow changed.
• No Dockerfile/Compose/scripts/runtime resources/endpoints/secrets/external targets/deployment/automation changed.
• No live cloud calls, credentials, or tenant targets added.
• PR Add next-level architecture skeleton #334 was not touched.

Not-proven boundaries:

• No production readiness/certification.
• No live-cloud or real-tenant validation.
• No benchmark/load/stress proof.
• No throughput/p95/p99 production evidence.
• No real-world latency improvement claim.
• No replay/export/storage proof.
• No broader automation.