test: improve prompt test maintainability

[hudrazine]

Summary

• derive status version expectations from package and Portable Core sources
• strengthen Extension prompt replacement assertions
• add focused coverage for Runtime Layer defaults, ordering, conditional guidelines, and empty sections
• keep Portable Core version and hash as an explicit acceptance gate

Why

Prevent routine package version bumps from requiring manual test edits while preserving intentional prompt-change detection and improving contract coverage.

Tests

• vp run check
• vp run test (18 tests)

No changeset is included because this is a test-only change.