[FEATURE] Add per-step AI Chat configuration

[MRawhani]

Is your feature request related to a problem? Please describe

CARE does not currently allow AI Chat hooks and context sources to be configured for individual workflow steps.

Describe the solution you'd like

Create a new workflow based on Peer Review Workflow (Assessment with AI) with AI Chat enabled for its Annotator and Editor steps.

Reuse CARE’s existing per-step service configuration and input-mapping flow:

workflow_step.configuration.services
→ study_step.configuration.services

During study creation:

• Select an AI Chat hook for each configured step.
• Map all required hook inputs.
• Annotator can use the studied document.
• Editor can use the same document and previous-step comments.
• Do not show output mapping or separate model configuration.
• Save and reload the selected hooks and mappings.

Runtime context behavior will be implemented separately:

• Shared sources are introduced once.
• Step-specific sources are introduced when first required.
• New context is appended as a system message.
• Once introduced, context remains available to the conversation.

Describe alternatives you've considered

Study-level configuration was rejected because AI Chat context sources may differ between steps.

Additional context

Complete when

A study can be created with valid AI Chat configuration for both steps, and all selected hooks and input mappings are saved and restored from the corresponding study_step.configuration.