fix(ui): prevent chat from aggressively scrolling to bottom on slash …

[Dhirenderchoudhary]

Description

Resolves #581.

Previously, rendering the slash command completions menu outside of the main bordered input <Box> altered the height of the live viewport area. This height change triggered Ink.js to recalculate flexbox layouts, forcing the chat history to unexpectedly snap to the bottom in smaller terminal windows.

This commit moves the rendering of both command completions and file suggestions inside the bounded layout. The container expands naturally without disrupting the overall window height calculation, keeping the user's scroll position intact.

Additionally:

• Adds structural layout tests verifying completions render inside the container.
• Fixes test timing flakes where simulated stdin input was occasionally ignored.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Testing

Automated Tests

• New features include passing tests in .spec.ts/tsx files
• All existing tests pass (pnpm test:all completes successfully)
• Tests cover both success and error scenarios

Manual Testing

• Tested with Ollama
• Tested with OpenRouter
• Tested with OpenAI-compatible API
• Tested MCP integration (if applicable)

Checklist

• Code follows project style guidelines
• Self-review completed
• Documentation updated (if needed)
• No breaking changes (or clearly documented)
• Appropriate logging added using structured logging (see CONTRIBUTING.md)