Fix gateway addition from UI

[madhav165]

🐛 Bug-fix PR

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📌 Summary

Gateway addition from UI is broken after admin API started treating any gateway with oauth_config as an oauth gateway. This was because UI was sending oauth_grant_type as authorization_code for all gateways irrespective of gateway auth_type. This led to all gateways being treated as oauth gateways.

💡 Fix Description

Makes oauth_grant_type as '' when auth_type in gateway submit and edit forms is ''.

🧪 Verification

Check	Command	Status
Lint suite	make lint	pass
Unit tests	make test	pass
Manual regression no longer fails	steps / screenshots	Tested with sse server with no auth

📐 MCP Compliance (if relevant)

• No breaking change to MCP clients

✅ Checklist

• Code formatted (make black isort pre-commit)
• No secrets/credentials committed

[kevalmahajan]

The tools are now fully populated for the added MCP server, and everything is fixed and works when authentication is not OAuth.