Update V1 to V2 migration tool for Foundry Agent Service guidance

[leestott]

Title
Update V1 to V2 migration tool for Foundry Agent Service guidance

Summary
This PR updates the migration solution to align the V1 to V2 migration flow with the current Microsoft Foundry Agent Service model. The migration target now uses versioned agent creation via create_version, validates migrated agents with conversations plus responses, and removes reliance on legacy assistant runtime patterns.

What Changed

• Reworked the main migration flow in migration v1_to_v2_migration.py to target Foundry Agent Service instead of legacy assistant-style write APIs.
• Standardized agent creation on explicit PromptAgentDefinition payloads and AIProjectClient.agents.create_version(...).
• Updated runtime validation to use project.get_openai_client() with conversations and responses rather than threads, runs, or legacy messages.
• Kept source ingestion flexible so migration can still read from the legacy API, project endpoints, project connection strings, or Cosmos DB.
• Refreshed migration documentation and configuration guidance in migration/README.md, migration/README-Docker.md, migration/.env.example, and migration/CHANGELOG.md.
• Cleaned up the Docker auth wrappers in migration/run-migration-docker-auth.ps1 and migration/run-migration-docker-auth.sh by removing stale legacy env passthrough, adding a real help-only path, and fixing Bash compatibility on Windows-hosted workspaces.
• Expanded offline regression coverage in migration/test_v1_to_v2_migration.py to cover wrapper help behavior and Bash syntax validation in addition to migration logic.

Behavioral Notes

• Unsupported classic tools are not silently dropped; the migration emits explicit warnings and recommendations.
• Post-migration test tool injection remains supported for function, MCP, computer use, image generation, and Azure Function scenarios.
• Historical threads, runs, and messages are still out of scope and are not migrated.

Validation

• Python compile checks passed for the migration tool and test module.
• Focused migration test suite passed: 11 passed.
• PowerShell wrapper help smoke check passed.
• Bash wrapper syntax validation with bash -n passed.

Known Limitations

• A live end-to-end Foundry dry run was not executed in this change set because the local environment did not contain a real source assistant plus production target configuration, and Docker was not available at validation time. Local validation and regression coverage are green.

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