docs: add Ecosystem section to README

[httpdss]

Issue

N/A - Documentation enhancement

Description

Added a new Ecosystem section to the README that highlights StructKit's various install paths and integrations. This section is positioned after the "Try it in 60 seconds" quickstart and before "Who StructKit is for" to give readers immediate visibility into the broader ecosystem.

The section includes:

• GitHub Action for CI validation, generation, and drift-checking
• VS Code / Cursor extension for schema validation and autocomplete
• Agent skills for AI assistant integration
• pre-commit hooks for validation
• Homebrew tap for macOS installation
• Backstage plugin for platform teams
• Hermes plugin for safe StructKit tooling

This change improves discoverability of the ecosystem tools and clarifies that these are install paths for StructKit, not separate products.

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)

N/A - Text documentation change

Additional Comments

This is a documentation-only change. No code or functionality has been modified. Only README.md was updated.