fix: ChatOpenAI baseOptions additional parameters not applied to model

[BOOPATB]

Problem

Fixes #2499

BaseOptions JSON input in the ChatOpenAI node was only being passed as
defaultHeaders inside configuration, meaning any model-level parameters
(e.g. stop, top_p) were silently ignored and never sent to the API.

Root Cause

In ChatOpenAI.ts, parsedBaseOptions was unconditionally assigned to
configuration.defaultHeaders, with no path to merge params into the model object.
Additionally, the merge happened after the reasoning model cleanup block, meaning
it could have re-introduced stop/temperature that were intentionally deleted.

Fix

• Destructure parsedBaseOptions into { defaultHeaders, baseURL, ...modelParams }
• Spread modelParams directly into obj so params like stop reach the model
• Move the baseOptions merge to before the reasoning model block so cleanup still works correctly
• Update the BaseOptions field description to reflect its actual capability

Testing

• Set { "stop": ["<|im_end|>"] } in BaseOptions on a ChatOpenAI node
• Confirm the stop sequence is respected in the model response
• Confirm reasoning models (o-series) still correctly strip stop/temperature
• Confirm defaultHeaders and baseURL inside BaseOptions still work for custom endpoints

[gemini-code-assist]

Code Review

This pull request updates the ChatOpenAI component to allow more flexible model parameter configuration via the baseOptions field and reorders the initialization logic to ensure reasoning model constraints are applied correctly. I have identified a security risk regarding mass assignment from user-provided JSON and a concern regarding inconsistent indentation introduced in the refactor.

[gemini-code-assist]

Avoid mass assignment from user-provided JSON to the model configuration object. Directly spreading modelParams into obj allows users to overwrite sensitive fields like apiKey or openAIApiKey, which are intended to be managed via credentials. Please explicitly exclude these sensitive fields to prevent potential security issues or unexpected behavior.

Suggested change

	const { defaultHeaders, baseURL, ...modelParams } = parsedBaseOptions
	// Spread extra model params (e.g. stop, top_p) into obj
	Object.assign(obj, modelParams)
	const { defaultHeaders, baseURL, apiKey, openAIApiKey, configuration, ...modelParams } = parsedBaseOptions
	// Spread extra model params (e.g. stop, top_p) into obj
	Object.assign(obj, modelParams)

References

1. Avoid mass assignment from request bodies to entities. Instead of using a generic assignment like Object.assign(entity, body), explicitly map allowed properties.

[BOOPATB]

Fixes #2499