Position StructKit as YAML scaffolding for AI assistants via MCP

[httpdss]

Issue

N/A - Documentation improvement

Description

Updated the README.md hero section to better position StructKit as YAML scaffolding for AI assistants via MCP rather than a generic YAML tool.

Key changes:

• Simplified title to "StructKit" (removed emoji and subtitle)
• New tagline: "YAML scaffolding your AI assistant can actually run"
• Clearer value proposition emphasizing MCP integration: define once, generate from CLI/CI/assistant
• Added structkit mcp --server command to the 60-second quick start
• Streamlined navigation links to focus on Quick Start, Docs, MCP Guide, and Discussions
• Kept all badges and the Docker example

What wasn't changed:

• Everything from "Who StructKit is for" section onwards remains unchanged
• All comparison tables, examples, documentation links, license, and support sections preserved
• No code, docs pages, or unrelated files modified

Outcome: Visitors now understand StructKit's MCP/AI assistant value in the first screen and can get to pip install + MCP server in under 60 seconds.

Checklist

• I have read the contributing guidelines.
• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works. (N/A - documentation only)
• New and existing unit tests pass locally with my changes. (N/A - documentation only)
• I have updated the documentation accordingly.

Screenshots (if applicable)

Before: README led with "YAML-first scaffolding for teams and AI agents"
After: README leads with "YAML scaffolding your AI assistant can actually run" and highlights MCP in the first 60 seconds

Additional Comments

This change focuses purely on repositioning the messaging to emphasize the MCP/AI assistant use case, which is the key differentiator for StructKit. All technical content, examples, and documentation links remain intact.