feat: delegate Foundry project ownership to projects

[Hui Miao (huimiu)]

Why this is needed

Foundry project identity, managed deployments, and infrastructure lifecycle were previously coupled to the agents extension. That made project reuse, configuration migration, and cross-extension behavior inconsistent. This change establishes a single owner for project-level resources while preserving agent-specific responsibilities.

Approach

The projects extension now owns Foundry project identity, deployment selection, environment reconciliation, and infrastructure synthesis/ejection. The agents extension delegates project operations through a versioned file-based WorkflowService contract, with structured error propagation and a legacy fallback for older projects extensions. Core azd adds the required environment mutation, project configuration, workflow, and structured error transport APIs.

The implementation also preserves unknown configuration fields and hooks, handles endpoint/resource-ID compatibility, filters deployment candidates by location and quota, and documents the new extension boundary and APIs.

Validation

• Passed source checks: gofmt, go fix, copyright, lint, cspell, cspell-misc, and build.
• Passed focused core, azure.ai.projects, and azure.ai.agents tests.
• Full preflight test/playback checks remain environment-blocked by an unavailable Docker daemon, missing recorded network interactions, and existing Windows-specific test failures.

[Hui Miao (huimiu)]

This PR is superseded by the reviewable native stack in PRs #9509 through #9513. It is being closed to avoid duplicate review of the same changes.