Hand the MCP SDK an authorization result with the issuer

mcp 2.x reads code, state and the RFC 9207 iss off the callback handler's
result; the handler still returned a (code, state) tuple, so every MCP
sign-in failed after the user approved it. The callback route now keeps the
issuer too, since servers that advertise it (Linear) refuse a sign-in
without it.

docsgpt/api/user/tools/mcp.py

@@ -539,7 +539,7 @@ class MCPOAuthCallback(Resource):
                     "/api/connectors/callback-status?status=error&message=Internal+server+error:+Redis+not+available.&provider=mcp_tool"
                 )
             manager = MCPOAuthManager(redis_client)
-            success = manager.handle_oauth_callback(state, code, error)
+            success = manager.handle_oauth_callback(state, code, error, iss=request.args.get("iss"))
             if success:
                 return redirect(
                     "/api/connectors/callback-status?status=success&message=Authorization+code+received+successfully.+You+can+close+this+window.&provider=mcp_tool"