Complete Pester 4 to Pester 5 migration audit across all test files

[johnmccrae]

Context

During ex10 we fixed tests/Common/Environment.tests.ps1 (bare Mock in Describe body, if-wrapped Describe). A full audit was not completed across all 15 test files. Any remaining Pester 4 patterns risk silent test failures or incorrect behaviour under Pester 5.

Acceptance Criteria

• All .tests.ps1 files audited for: bare Mock/MockWith outside BeforeAll/BeforeEach/It, if blocks wrapping Describe, Assert-MockCalled (Pester 4 assertion)
• Any findings fixed and verified with Invoke-Pester locally
• Zero Pester warnings about legacy parameter sets in CI output

Relevant Code Paths

• tests/Unit/*.tests.ps1
• tests/Common/*.tests.ps1
• tests/Acceptance/Project.Tests.ps1
• tests/Integration/Templates.Integration.Tests.ps1

Dependency

None — can be done independently.