0.9.0 is here!!!!!!!!!

• Full theme configuration schemas with validation and defaults
• Per-page configuration overrides through frontmatter
• Environment-aware development and production configuration
• Extended head management for scripts, metadata, and Open Graph tags
• New Marketing Minimal theme
• Redesigned Docs Minimal with a consistent theme design language
• Expanded Tau security, unit tests, and real-site integration coverage
• Bump marked from 18.0.6 to 18.0.7