* fix: Set response format for agent tools in DALLE3, FluxAPI, and StableDiffusion classes
- Added logic to set `responseFormat` to 'content_and_artifact' when `isAgent` is true in DALLE3.js, FluxAPI.js, and StableDiffusion.js.
* test: Add regression tests for image tool agent mode in imageTools-agent.spec.js
- Introduced a new test suite for DALLE3, FluxAPI, and StableDiffusion classes to verify that the invoke() method returns a ToolMessage with base64 in artifact.content, ensuring it is not serialized into content.
- Validated that responseFormat is set to 'content_and_artifact' when isAgent is true, and confirmed the correct handling of base64 data in the response.
* fix: handle agent error paths and generateFinetunedImage in image tools
- StableDiffusion._call() was returning a raw string on API error, bypassing
returnValue() and breaking the content_and_artifact contract when isAgent is true
- FluxAPI.generateFinetunedImage() had no isAgent branch; it would call
processFileURL (unset in agent context) instead of fetching and returning
the base64 image as an artifact tuple
- Add JSDoc to all three responseFormat assignments clarifying why LangChain
requires this property for correct ToolMessage construction
* test: expand image tool agent mode regression suite
- Add env var save/restore in beforeEach/afterEach to prevent test pollution
- Add error path tests for all three tools verifying ToolMessage content and
artifact are correctly populated when the upstream API fails
- Add generate_finetuned action test for FluxAPI covering the new agent branch
in generateFinetunedImage
* chore: fix lint errors in FluxAPI and imageTools-agent spec
* chore: fix import ordering in imageTools-agent spec
