docs: clarify Foundry resource group constraint

[lntutor]

What does this PR do?

Clarifies that --resource-group is required when --resource-name is passed to azmcp foundryextensions resource get. It also updates the command summary to describe the returned resource metadata.

Closes #2978

GitHub issue number?

#2978

Validation

• dotnet build servers/Azure.Mcp.Server/
• dotnet build tools/Azure.Mcp.Tools.FoundryExtensions/src/
• dotnet test tools/Azure.Mcp.Tools.FoundryExtensions/tests/Azure.Mcp.Tools.FoundryExtensions.Tests/ --filter "TestType!=Live" (80 passed)
• git diff --check

The PowerShell spelling wrapper could not run because pwsh is unavailable locally; the direct Node fallback is also blocked by a broken local Homebrew simdjson linkage.

Pre-merge Checklist

• Required for All PRs
  • Read contribution guidelines
  • PR title clearly describes the change
  • Commit history is clean with descriptive messages
  • Tests are not required for this documentation-only correction
  • Changelog entry is not required for this documentation-only correction
• Extra steps for Azure MCP Server documentation changes:
  • Updated command list in servers/Azure.Mcp.Server/docs/azmcp-commands.md
  • Reviewed the change for security vulnerabilities or suspicious content

[azure-pipelines]

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[github-actions]

Thank you for your contribution @lntutor! We will review the pull request and get back to you soon.

[Copilot]

Pull request overview

This PR updates the Azure MCP Server command reference to document the foundryextensions resource get parameter constraint introduced in prior code changes, and clarifies what metadata the command returns so users/agents don’t hit an unexpected runtime validation error.

Changes:

• Document that --resource-group is required when --resource-name is specified for azmcp foundryextensions resource get.
• Refine the command’s one-line summary to emphasize it returns Foundry resource metadata (e.g., endpoint/SKU/location).

[lntutor]

Current head 52b549e is mergeable, and the only visible blocker I can see as of August 1, 2026 is the Azure Pipelines mcp - pullrequest (Build Build macos_x64) leg from July 31, 2026. The failure is in Azure.Mcp.Server.Tests.Infrastructure.ConsolidatedModeTests.ConsolidatedMode_HttpTransport_Should_Reject_Request_Without_McpMethod_Header, which timed out waiting for the Azure MCP HTTP endpoint and then hit Connection refused (127.0.0.1:49555); the other Azure build legs, CLA, and event-processor checks are green on this same head. Since this PR only updates Azure MCP command documentation and does not touch that server test area, this looks like an external/unrelated current-head blocker rather than remaining contributor-side docs work. If that macOS leg is known flaky, a maintainer rerun/review should be enough to unblock it.