Add streamable HTTP transport support with examples for local and remote servers

[Copilot]

This PR adds comprehensive support for streamable HTTP transport to address the deprecation of SSE, providing modern HTTP transport capabilities with examples for both local and remote server usage.

Changes Made

Core Transport Implementation

• Added --transport flag supporting http (streamable), sse, with http as default
• Updated client creation logic to use NewStreamableHttpClient for HTTP URLs
• Maintained full backward compatibility with existing SSE transport via --transport=sse
• Enhanced flag processing to handle transport selection

Server Template Support

• Created templates/ts/server_http.ts using StreamableHTTPServerTransport
• Implemented session management with UUID generation for stateful connections
• Added proper Express.js integration with JSON body parsing
• Updated mcp new command to support --transport=http option

Documentation & Examples

• Added comprehensive streamable HTTP transport section to README
• Provided step-by-step examples for local server creation:

  # Create and run a local streamable HTTP server
  mkdir my-http-server && cd my-http-server
  mcp new tool:example_tool --transport=http
  npm install && npm run build && npm start

• Added examples for connecting to remote servers:

  # Connect to local or remote streamable HTTP servers
  mcp tools http://localhost:3000
  mcp tools https://api.example.com/mcp
  
  # Use SSE for legacy servers
  mcp tools --transport=sse http://legacy-server.com/sse

Testing & Validation

• Added unit tests for transport flag processing and URL validation
• Verified all existing functionality remains intact (100% backward compatibility)
• Validated template generation for all transport types (stdio, sse, http)
• Confirmed generated projects compile and run successfully

Key Benefits

1. Modern Transport: Streamable HTTP is now the recommended approach, addressing SSE deprecation
2. Session Management: Supports stateful connections with automatic session ID generation
3. Flexibility: Supports both streaming responses and direct JSON responses
4. Developer Experience: Complete tooling for creating and connecting to streamable HTTP servers
5. Backward Compatibility: Existing SSE-based workflows continue to work unchanged

Usage Examples

Create a local streamable HTTP server:

mcp new tool:calculator --transport=http
cd calculator && npm install && npm run build && npm start

Connect to servers:

# Default streamable HTTP
mcp tools http://localhost:3000

# Explicit transport selection
mcp tools --transport=http https://remote-mcp-server.com
mcp tools --transport=sse http://legacy-server.com/sse

The implementation leverages the existing NewStreamableHttpClient function in mcp-go v0.24.1 and the StreamableHTTPServerTransport class in the MCP TypeScript SDK, providing a complete solution for modern MCP transport needs.

Fixes #56.

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