feat: add accessible flag and environment variable for screen reader friendly forms

[srtaalej]

Changelog

Interactive forms become screen reader friendly when the ACCESSIBLE environment variable is set or when using the --accessible flag.

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.

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.22%. Comparing base (955c925) to head (4f13099).

Files with missing lines	Patch %	Lines
cmd/root.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #455      +/-   ##
==========================================
- Coverage   71.23%   71.22%   -0.02%     
==========================================
  Files         222      222              
  Lines       18664    18678      +14     
==========================================
+ Hits        13295    13303       +8     
- Misses       4189     4192       +3     
- Partials     1180     1183       +3     

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[zimeg]

@srtaalej So amazing to find this feature arriving here! 🍀 ✨

Before approving I want to leave a few comments, but think we can follow up with some other improvements to the edges:

• Environment Variable: The ACCESSIBLE environment variable is standard I understand and we should include support alongside these changes! This makes preferring these prompts easier with an export added to the shell profile 🔬
• Blank Selections: The "select" prompts request a number to be entered but accept blank input for the first option! This might be an upstream issue 🐛
• Input Default: Adjacent for the "input" prompt I find the default value of the create command name isn't showing 🧪

The first note is most important for these changes IMHO! I'd be curious if the latter two can be proven in unit tests, but please don't consider those blocking 🙏

[zimeg]

🌲 thought: As we're introducing this, should we include the environment variable similar?

ACCESSIBLE

We recommend setting this through an environment variable or configuration option to allow the user to control accessibility.

🔗 https://github.com/charmbracelet/huh?tab=readme-ov-file#accessibility

[zimeg]

🔍 ramble: We might find this adjacent file most useful!

slack-cli/internal/config/dotenv.go

Lines 23 to 24 in f39d175

	// LoadEnvironmentVariables sets flags based on their environment variable value
	func (c *Config) LoadEnvironmentVariables() error {

[zimeg]

@srtaalej Thanks for these updates! I'm hoping we can land a few more to bring this to a polished state for release 🔬 ✨

I tested some more cases that I'll share here:

• One selection option: The hint is solid IMHO! I share more comments on the title format later but I'm a fan of the hint.

• Multiple select options: This highlights the ":" format a bit more for following comments.

• Invalid select options: Super cool that this validates!

• Confirmation default: This appears as a kind callout.

• Input prompts without default: These might favor the trailing ":" also?

The formatting issue I callout in comments below and some screenshots above is that I think form titles should end with a ":" to signal input! Some workarounds might be needed in code but this outputs well I think.

Let me know if more testing can be requested 🫡

[zimeg]

Suggested change

	title = fmt.Sprintf("%s (default: %s)", message, cfg.Placeholder)
	title = fmt.Sprintf("%s (default: %s):", strings.TrimSuffix(message, ":"), cfg.Placeholder)

🔭 suggestion: This might not be the right syntax but I think formatting input ends best with a colon:

- Name your app: (default: flamboyant-salamander-784)
+ Name your app (default: flamboyant-salamander-784):

[zimeg]

🎨 ramble: We don't have a comment on this in the STYLE_GUIDE at this time and we're not consistent on using a : at all or sometimes ? instead. This might be something nice to align over time.

[zimeg]

Suggested change

	title = fmt.Sprintf("%s (press Enter for 1)", msg)
	title = fmt.Sprintf("%s (press Enter for 1):", strings.TrimSuffix(msg, ":"))

🪬 suggestion: Similar to the : suggestion above - I'm more hesitant to this one because some titles might end with "?" but I don't think that formatting is incorrect...