fix: align custom application hooks and private validation fixtures

[Paulo Lacerda (placerda)]

Changes

• Normalize directory/file application-definition selections in PowerShell and Bash.
• Deploy each declared service from the definition folder's azure.yaml; retain source-commit verification in its source folder and reuse the azd environment.
• Select the declared hosted greeting protocol and explicitly target the service. Validate raw Responses JSON/SSE without weakening bundled Invocations completion checks.
• Make the hosted sample return a completed assistant message.
• Narrow VM SKU preflight requests to virtualMachines.
• Preserve the ACR Task pool guard; positive fixtures provide a pool and negative cases cover missing pools and local builds.

Evidence

• python -m pytest -q tests: 386 passed, 4 skipped, 462 subtests passed.
• python -m unittest discover -s tests: 355 passed, 2 skipped.
• Infrastructure preflight: 73 of 75 assertions passed; both failures also reproduce on unchanged HEAD (empty-Boolean parameter expansion). The two new SKU assertions pass.
• The consolidation merge preserved the exact tested source tree.
• Central docs: docs: clarify custom application project and smoke contracts AI-Landing-Zones#148.

Azure acceptance status

These fixes do not retroactively validate v4.2.2. T035/T085/T098/T093 remain open. Classic foundation provisioned but post-provision governance failed because public Key Vault access was disabled and no private endpoint exists for that vault. Hosted retry and private-foundation evaluation continue separately. No security policy was disabled.