Add pre-flight version check for registry stdio servers

[jongio]

Problem

When azd is installed but at a version below the minimum (1.20.0), the error message says "This tool may require dependencies that are not installed" instead of telling the user their version is too old. This is confusing — the tool IS installed, just outdated.

Fixes #1025

Solution

Add a generic pre-flight version check to RegistryServerProvider that runs before creating the stdio MCP client. Registry servers can now declare minVersion and versionArgs in registry.json to enable version checking.

Error messages are now specific:

• Not installed: 'azd' is not installed or not found in the system PATH.
• Wrong version: 'azd' version 1.11.0 is installed, but version 1.20.0 or later is required.

Changes

File	Change
RegistryServerInfo.cs	Added MinVersion and VersionArgs properties
RegistryServerProvider.cs	Added CheckCommandVersionAsync with 30s timeout, concurrent stdout/stderr reading, proper process cleanup; added ParseVersionFromOutput with GeneratedRegex
registry.json	Added minVersion: 1.20.0 and versionArgs: ["version"] for azd
RegistryServerProviderTests.cs	Added 7 tests covering: version parsing, command-not-found, version-too-old, version-sufficient, CreateClientAsync integration

Design Decisions

• Generic, not azd-specific: Any stdio registry server can use minVersion/versionArgs
• Fail-open: If version check encounters unknown errors or times out, it falls through to the normal connection attempt
• 30s hard timeout: Prevents a hung version command from blocking indefinitely
• Process safety: Concurrent stdout+stderr reading (prevents pipe-buffer deadlocks), Process.Kill(entireProcessTree: true) on timeout, Process.Start() return value checked
• AOT safe: Uses [GeneratedRegex] for source-generated regex

Testing

• 21 tests pass (14 existing + 7 new)
• 0 build warnings
• Format verified clean

Invoking Livetests

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[Copilot]

Pull request overview

Adds a generic pre-flight version check for registry-defined stdio MCP servers so users get a clear, actionable error when a required dependency is installed but below a minimum version (e.g., azd < 1.20.0), addressing the confusion described in #1025.

Changes:

• Extended registry server configuration to support minVersion and versionArgs.
• Added process-based version probing + version parsing in RegistryServerProvider before creating stdio clients.
• Updated the built-in registry.json entry for azd to require >= 1.20.0 and added unit tests covering parsing and common failure/success cases.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
servers/Azure.Mcp.Server/src/Resources/registry.json	Declares azd’s minimum required version and how to query it.
core/Microsoft.Mcp.Core/src/Areas/Server/Models/RegistryServerInfo.cs	Adds MinVersion / VersionArgs to the registry server model.
core/Microsoft.Mcp.Core/src/Areas/Server/Commands/Discovery/RegistryServerProvider.cs	Implements the pre-flight version check and version parsing logic used during client creation.
core/Azure.Mcp.Core/tests/Azure.Mcp.Core.UnitTests/Areas/Server/Commands/Discovery/RegistryServerProviderTests.cs	Adds tests for version parsing and version-check behavior paths.