feat: AI-assisted workflow builder

[rperaltaster-code]

Overview

Let users describe a workflow in plain English and have AI generate the initial step structure. Lowers the barrier to entry for non-technical users.

Goals

• Text prompt input: "Create an employee onboarding workflow with manager approval and IT notification"
• AI generates a structured step list (type, name, config, order)
• Steps are loaded into the visual builder for review and editing
• Users can iterate ("add a delay before the notification step")

Acceptance Criteria

• /api/workflows/ai-generate endpoint accepts a prompt, returns step definitions
• Claude API (claude-sonnet-4-6) used for generation with structured output
• Builder UI has an "Generate with AI" entry point
• Generated steps are editable before saving
• Fallback gracefully if AI generation fails

Notes

Depends on having a solid manual builder first. Condition branching (#6) and forms (#1) should be in place before AI generation is reliable enough to be useful. Use claude-sonnet-4-6 model.