[AI-BUILDER-3] (frontend): preview generated steps

[kevinkim-ogp]

TL;DR

Adds a new AI Builder page that allows users to preview the AI-generated steps, with a multi-step loader component to display progress during generation.

What changed?

• Created a new MultiStepLoader component that shows animated loading states with progress indicators
• Added a new AiBuilder page with context provider to manage state for AI-generated workflows
• Implemented StepsPreview to display AI-generated steps with support for nested structures like If-Then and ForEach
• Added toolbox helper functions to handle step grouping and structure
• Created a modal for modifying AI prompts and regenerating workflows
• Added routing for the AI Builder at /editor/ai

How to test?

1. Create a Pipe using 'Build with AI'
2. Enter the workflow description and click on 'Create'
3. Verify redirection to /editor/ai
4. Verify that you see the multi-step loader while the steps are being generated
5. Review the generated workflow steps in the preview
6. Test the "Make changes" button to modify the prompt and regenerate the workflow
7. Verify that nested structures (If-Then, ForEach) display correctly

[kevinkim-ogp]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• [AI-BUILDER-15] PLU-605: chat feedback #1352
• [AI-BUILDER-14] feat: adds AI suggestions for form inputs #1364
• [AI-BUILDER-13] (frontend): refactor form modal content #1311
• [AI-BUILDER-12] (frontend): chat readiness check for steps preview #1363
• [AI-BUILDER-11] (frontend): preserve chat history and refactor #1365
• [AI-BUILDER-10] (backend): add chat readiness check #1362
• [AI-BUILDER-9] PLU-604 (frontend): Preview steps and create Pipe #1310
• [AI-BUILDER-8] PLU-603 (frontend): Chat interface #1309
• [AI-BUILDER-7] PLU-584 (backend): add api for chat streaming #1307
• [AI-BUILDER-6] PLU-584 (backend): setup api route #1306
• [AI-BUILDER-5] (frontend): add ai related deps #1305
• [AI-BUILDER-4]: create pipe from generated steps #1304
• [AI-BUILDER-3] (frontend): preview generated steps #1361 👈 (View in Graphite)
• [AI-BUILDER-2] PLU-595 (frontend): enter prompt #1303
• [AI-BUILDER-1] PLU-583 (backend): mutation to generate AI steps #1302
• [AI-2] PLU-583 (feat): add deps for AI and tracing #1360 : 1 other dependent PR (#1312 )
• [AI-1] (chore): bump zod and typescript #1359
• trunk/ai

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