feat(web): add kiosk mode for simplified UI

[cboecking]

Summary

Add kiosk mode to the web UI that provides a simplified user experience by hiding navigation elements.

URL Parameters

Parameter	Description
?kiosk=true	Hides sidebar and header
?dir=/path	Auto-opens project and navigates to new session

Use Cases

• Embedded deployments
• Simplified onboarding experiences
• Kiosk terminals
• Single-project focused workflows

Example URLs

# Basic kiosk mode
http://localhost:4096/?kiosk=true

# Kiosk with auto-project
http://localhost:4096/?kiosk=true&dir=/home/user/my-project

Changes

• packages/app/src/context/layout.tsx - Added kiosk.enabled() and kiosk.dir() state
• packages/app/src/pages/layout.tsx - Conditional sidebar rendering
• packages/app/src/components/session/session-header.tsx - Conditional header rendering
• packages/app/src/pages/home.tsx - Auto-redirect logic for dir parameter
• docs/KIOSK_MODE.md - Feature documentation

Test Plan

• Verify ?kiosk=true hides sidebar (desktop)
• Verify ?kiosk=true hides sidebar (mobile)
• Verify ?kiosk=true hides header
• Verify ?dir=/path auto-redirects to new session
• Verify normal mode unaffected without parameters
• Type checking passes

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[adamdotdevin]

Mind sharing a screenshot?

[cboecking]

Hi @adamdotdevin, thank you for your quick consideration!

The below screenshot is as a result of putting the following in the url:
http://localhost:3000/?url=http://127.0.0.1:4096&kiosk=true&dir=/home/debian/code/opencode

[cboecking]

Here is a screenshot when no dir/project is specified.

[cboecking]

It is worth noting the use case that prompted this change:

• I engage a business partner in a needs analysis meeting
• After the meeting, I realize there are gaps in our plan
• We document the plan and the gaps in a markdown file
• We launch opencode with an agent that describes how to annotate the document to close the gaps
• We send the url to the business partner with both kiosk enabled and the target directory where the markdown file exists.
• The expectation is that the business partner use opencode to close the gaps and verify the plan.