[CoR] Make deployment strategy service-specific and Flex-safe

[nturinski]

Problem

The deployment plan currently has one top-level deployStrategy, even though a project can contain application services with different deployment channels, such as Static Web Apps, Azure Functions Flex Consumption, App Service, and container hosts. Generic language-level Oryx guidance can consequently be applied to Flex Functions, where settings such as SCM_DO_BUILD_DURING_DEPLOYMENT and ENABLE_ORYX_BUILD are invalid.

Proposed work

• Add deployStrategy to each PlannedService.
• Introduce explicit channel-oriented values, for example:
  • functions-flex-package
  • appservice-oryx
  • appservice-startup-install
  • container-image
  • static-content
• Retain the current top-level strategy temporarily as a deprecated compatibility fallback for older plan artifacts.
• Update scaffold/deploy agents to consume each service's strategy and apply legacy Oryx settings only to compatible App Service targets.
• Add hard validation that rejects Oryx/SCM build settings for Flex Consumption.
• Update fixtures and documentation to remove ambiguous descriptions such as labeling a Flex package flow oryx-auto.

Likely implementation surfaces include:

• resources/agents/azure-deploy/prepare/references/prepare-schemas.ts
• resources/agents/azure-deploy/prepare/references/deploy-strategy.md
• resources/agents/azure-deploy/scaffold/references/bicep-functions-flex.md
• resources/agents/azure-deploy/deploy/references/code-deployment-functions-flex.md
• test/testProjects/copilotOnRails/scrapbook/prepare-plan.json

Acceptance criteria

• Every application service can carry its own deployment strategy.
• Mixed-hosting projects use the correct strategy for each service.
• Flex Consumption plans reject Oryx and SCM remote-build settings before provisioning.
• Existing plan artifacts with only the top-level strategy remain readable during the compatibility period.
• Newly generated plans use service-level strategies.
• Tests cover mixed-service plans, legacy fallback, and invalid Flex settings.