feat: multi-transport support for concurrent stdio/SSE/HTTP Stream

[QuantGeekDev]

Summary

Closes #124

• Adds transports array config to MCPServerConfig for running multiple transports concurrently from a single server instance
• Introduces TransportBinding model: each transport gets its own SDK Server instance, all sharing the same tool/prompt/resource registrations
• Validates config at construction: mutual exclusion of transport/transports, at most one stdio, no port conflicts
• Per-invocation tool.injectServer(targetServer) in the CallTool handler routes progress/sampling through the correct transport
• sendLog() broadcasts to all connected transports
• Full backward compatibility: existing transport: { type: 'stdio' } config works identically

Example usage

const server = new MCPServer({
  transports: [
    { type: "stdio" },
    { type: "sse", options: { port: 3001 } },
    { type: "http-stream", options: { port: 8080 }, auth: { provider: oauthProvider } },
  ],
});
await server.start();

Test plan

• 99 new tests across 4 test files (config validation, lifecycle parity, injectServer parity, e2e compat)
• All 781 existing tests pass unchanged (zero regressions)
• TypeScript compiles cleanly
• Manual test: start server with stdio + HTTP Stream, connect via both

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