feat: http mode for github mcp server.

[atharva1051]

Summary

Adds HTTP server mode enabling multi-tenant deployments where each client provides their own GitHub token via Authorization: Bearer <token> header.

Why

Enterprise scenarios require centralized MCP infrastructure serving multiple authenticated clients concurrently, which stdio mode's single-token-per-process model cannot support.

What changed

• Added http subcommand with --port flag (default 8080)
• Implemented RunHTTPServer() using MCP SDK's StreamableHTTPHandler
• Per-request token extraction from Authorization header
• HTTPServerConfig struct for HTTP-specific configuration
• Exposed port 8080 in Dockerfile
• Comprehensive documentation: VS Code/Claude Desktop configs, Docker deployment, GHES/GHEC support, security considerations

MCP impact

• No tool or API changes

HTTP mode uses existing tools—only the transport and authentication model changed.

Prompts tested (tool changes only)

N/A

Security / limits

• Auth / permissions considered

Tokens validated per-request, never stored. Each client's token creates isolated server instance with their permissions. Token scope filtering applied for PAT tokens.

Tool renaming

• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Updated (README / docs / examples)

Added HTTP mode section to README with client configuration examples (VS Code, Claude Desktop), Docker deployment patterns (basic, production with docker-compose), and troubleshooting guide.