feat(MssqlMcp/Node): Add multi-client HTTP/SSE transport and fix authentication fallback

[tripathishivani]

This PR enhances the Node.js implementation of the MSSQL MCP Server by adding support for HTTP streaming via Server-Sent Events (SSE). This allows the server to be accessed remotely over a network or via cloud-based AI agents, rather than strictly as a local child process. Additionally, it resolves a bug in the database connection configuration where standard SQL authentication and Azure AD authentication were conflicting.

Key Changes
HTTP/SSE Transport (--sse): Added an optional command-line flag to boot the server using an HTTP streaming interface.

Multi-Client Architecture: Implemented a session-routing system using an activeTransports Map. This allows multiple clients to connect simultaneously without their data streams colliding. It includes memory cleanup on client disconnect (res.on('close')).

Zero New Dependencies: The HTTP server, CORS handling, and URL parsing were implemented using Node.js native http and url modules to keep package.json lightweight.

Authentication Fix: Refactored createSqlConfig() to properly branch between authentication methods. It now cleanly falls back to Standard SQL Auth if SQL_USER and SQL_PASSWORD are present in the environment, rather than forcing the InteractiveBrowserCredential popup simultaneously.

Early Env Loading: Added dotenv.config() at the top level to ensure environment variables are reliably loaded before initialization.

Backward Compatible: The default behavior (running the script without flags) remains completely unchanged, defaulting to the stdio transport. Output logging for the HTTP server uses console.error() to protect the stdio JSON-RPC stream.

How to Test
Build the project: npm run build

Test Legacy Stdio Mode: npm start

Test New SSE Mode: node dist/index.js --sse
Optionally test with a custom port: node dist/index.js --sse --port 8080