Add support for creating stateless backends

[StpMax]

This PR adds the ability to generate and run stateless backend applications.
This is the simplest possible solution with minimal additions to the system prompt. However, it works quite stably for small tasks. The solution will be improved in the future.

Here's how it works:

• Artifacts should be generated in a separate folder, so the server .py file and frontend HTML will be located in the same directory.
• The agent should create a specification for the frontend/backend/API (note: without instructions on how to create the specification, the agent usually makes it very brief)
• The agent implements the artifacts and runs the backend in the scratchpad with action='serve', which immediately returns control to the main loop.

[entelligence-ai-pr-reviews]

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Confidence Score: 5/5 - Safe to Merge

Safe to merge — this PR adds support for creating stateless backends and has passed automated review with no issues identified. The implementation appears clean with no logic bugs, security concerns, or correctness problems flagged by either static analysis or manual review. No pre-existing unresolved comments are associated with this change.

Key Findings:

• Automated heuristic analysis found zero critical, significant, or medium-severity issues across all modified files.
• No new review comments were generated, suggesting the code follows established patterns and introduces no obvious regressions or edge-case concerns.
• The PR scope is focused — adding stateless backend support is a well-defined feature that does not appear to introduce side effects into existing stateful backend paths.

[torrmal]

this is good, we need to make sure tihs work all the way to this repo https://github.com/mindsdb/cowork
as that one assumes the artifacts hav e aspecific location, etc.
in that cowork repo, it would be amazing if there was a proxy endpoint for scratchpad:server endpoints, so all requests from the artifact are going thorugh an endpoint that later we can secure with some sort of authentication for sharing,
@StpMax