Streamable http support

[kevalmahajan]

✨ Feature / Enhancement PR

🔗 Epic / Issue

#109
Closes #109

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🚀 Summary (1–2 sentences)

Implemented streamable HTTP transport to enable client communication with the MCP gateway with authentication.

Added new variables in env:

• USE_STATEFUL_SESSIONS
  Set to False to use stateless sessions without an event store.
  Set to True for stateful sessions.

• JSON_RESPONSE_ENABLED
  Set to True to enable JSON responses.
  Set to False to enable SSE streams.

To test this out:

1. Open the MCP Inspector and Select "Streamable HTTP" as the transport option.
2. Enter the URL: http://localhost:4444/mcp/
3. Paste the Bearer authentication token for the gateway. Click on "Connect."

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🧪 Checks

• make lint passes
• make test passes
• CHANGELOG updated (if user-facing)

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[crivetimihai]

Merging intermediate PR