feat(inquirerer): add event-driven UI engine for custom prompts

[pyramation]

feat(inquirerer): add event-driven UI engine for custom prompts

Summary

Adds a new ui module to inquirerer that provides an event-driven engine for building rich terminal interfaces. This enables developers to create custom interactive UIs beyond the standard prompt types.

New components:

• UIEngine - Core engine with render/reducer pattern for custom screens
• Spinner - Animated loading spinner with multiple styles (dots, line, arc, etc.)
• ProgressBar - Visual progress indicator for operations with known completion
• StreamingText - AI-style streaming text display with cursor animation
• interactiveUpgrade - pnpm-style interactive dependency upgrade UI

Demo scripts:

• pnpm dev:spinner - Demonstrates spinner styles and states
• pnpm dev:chat - Simulates AI chat with streaming responses
• pnpm dev:upgrade - Interactive package upgrade selection

Review & Testing Checklist for Human

• Run all three demos manually (pnpm dev:spinner, pnpm dev:chat, pnpm dev:upgrade) - these were only briefly tested and the upgrade demo wasn't tested at all
• Verify terminal cleanup - After running demos, ensure cursor is visible and terminal is in normal state. Also test CTRL+C during each demo to verify cleanup on interrupt
• Test upgrade UI edge cases - Type a filter that matches nothing, navigate with arrow keys, verify no crashes (similar to the checkbox bug we fixed earlier)
• Review the empty dispatch method in engine.ts (line 218) - it's a stub for future async event dispatch
• Note: No automated tests were added for this new feature

Recommended test plan:

1. Run pnpm build in the inquirerer package
2. Run each demo script and interact with it
3. Press CTRL+C during each demo to verify cleanup
4. In the upgrade demo, try filtering, selecting packages, and pressing ESC to cancel

Notes

• The package.json has a minor indentation change in the scripts section
• The Spinner class accepts a UIEngine in constructor but doesn't use it (may be for future extensibility)
• This is ~1600 lines of new code without unit tests - consider adding tests before publishing

Link to Devin run: https://app.devin.ai/sessions/e424b0eaba2f4789815bb0cc22ca6233
Requested by: Dan Lynch (@pyramation)

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring