refactor(gateway): migrate MCP implementation to ModelContextProtocol…

[GreenShadeZhang]

Description

This PR refactors the Gateway MCP server implementation to use the official ModelContextProtocol C# SDK and removes the legacy hand-rolled JSON-RPC endpoint implementation.

Problems solved:

• Reduces protocol maintenance burden from custom MCP routing/envelope handling.
• Aligns Gateway MCP behavior with SDK-native MCP transport/capability handling.
• Keeps the existing OpenClaw MCP capability surface (tools/resources/prompts) while simplifying implementation structure.
• Preserves MCP auth and rate-limit protections on /mcp.

Key changes:

• Replaced legacy Endpoints/McpEndpoints.cs with SDK-based MCP registration.
• Added SDK-based MCP modules under Mcp:
  • OpenClawMcpTools
  • OpenClawMcpResources
  • OpenClawMcpPrompts
  • McpSdkExtensions
  • GatewayRuntimeHolder
• Wired SDK route and middleware in Program.cs (MapMcp("/mcp"), MCP auth/rate-limit path).
• Updated service registration and endpoint mappings to remove old MCP endpoint path.

AOT note:

• Current SDK integration path relies on reflection-based discovery, so Gateway MCP is currently configured for non-AOT publishing in this refactor.

Related Issues

• Contributes to MCP SDK migration effort in Gateway.
• No direct issue number linked yet.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Checklist

• I have read the CONTRIBUTING guidelines
• My code follows the code style implementation of this project
• I have added tests that prove my fix is effective or that my feature works
• All new and existing tests passed locally (dotnet test)
• I have updated the documentation (README.md, comments) if required
• I have checked for security implications (input validation, authorization)

Validation performed:

• dotnet build OpenClaw.Gateway.csproj -c Release

Screenshots (if applicable)

Benchmarks (if applicable)

No benchmark run for this refactor.
Expected runtime impact is neutral to minor overhead differences depending on SDK transport internals.