feat: integrate Clay UI Layout Library as optional layout engine

[pbisogno]

Add Clay (C Layout) as a new layout option for OTUI screens, coexisting with the existing anchor, horizontal, vertical, grid, and flexbox layouts.

• Vendor clay.h v0.14 (single-header, MIT licensed, zero dependencies)
• New UIClayLayout class bridging Clay's layout engine with UIWidget
• OTUI support via layout: clay with direction, child-gap, align-x/y
• Lua bindings for programmatic layout creation
• CMake toggle TOGGLE_FRAMEWORK_CLAY (ON by default)
• Demo module (client_claydemo) with button on top menu for testing

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Behavior

Actual

Do this and that doesn't happens

Expected

Do this and that happens

Fixes

# (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B

Test Configuration:

• Server Version:
• Client:
• Operating System:

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I checked the PR checks reports
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works