fix(kv-skills):reorg, group and update skills, add initial page design audit skill

[mcstover]

This pull request expands the Kiva skills plugin system by introducing two new plugin categories—kiva-design-to-code and kiva-skill-builder-utils—and updates the documentation and marketplace files to reflect these additions. It also refines the descriptions and documentation for the existing kiva-design-system plugin, clarifying its purpose and improving cross-references to related skills.

Marketplace and Plugin Structure Updates:

• Added kiva-design-to-code and kiva-skill-builder-utils as new plugin categories in both .agents/plugins/marketplace.json and .claude-plugin/marketplace.json, making them available for installation and use. [1] [2]
• Updated the @kiva/kv-skills/README.md to document the new plugin categories, their purposes, and to clarify the structure of the plugin folders. [1] [2]

Design System Plugin Enhancements:

• Revised the descriptions, keywords, and version numbers in kiva-design-system plugin manifests for both Claude and Codex, focusing the messaging on using the design system and updating to version 0.2.0. [1] [2]
• Updated the @kiva/kv-skills/design-system/README.md to clarify the plugin's role as the entry point for using the design system, and to direct users to the new plugins for code migrations and skill-authoring tooling. [1] [2] [3]

Documentation Improvements and Cross-References:

• Updated all references in design system skill markdown files (e.g., color, layout, radius, spacing) to point to the new kiva-design-to-code plugin and its kiva-tailwind-css skill, improving clarity on where to find implementation details and setup instructions. [1] [2] [3] [4] [5] [6] [7]
• Added a clarification in the typography documentation about the intended use of the "Display" style, emphasizing its use for marketing pages only.