Changelog

Added --accessible flag for screen reader friendly prompts

Summary

Related: #454
This PR adds a global --accessible flag that switches huh interactive prompts to accessible mode. In accessible mode, select prompts render as numbered lists with "Enter a number between 1 and N" input, confirm prompts accept y/n text, and input prompts use plain line-by-line I/O. This makes the CLI usable with screen readers by avoiding the TUI-based rendering

Test plan

Run slack create --accessible and verify prompts render as numbered lists
Run slack login --accessible and verify confirm prompt accepts y/n
Run slack create (without flag) and verify normal TUI prompts still work
go test ./internal/iostreams/ -run TestFormsAccessible

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.