Update docs to Material theme and 1.0 compatibility

[abrookins]

Summary

Updates the documentation site with a modern Material for MkDocs theme and ensures all code examples are compatible with Redis OM 1.0.

Changes

Theme & Structure

• Switch to Material for MkDocs theme with Redis branding (red color scheme, dark/light mode)
• Add custom styling for code blocks, tables, and feature cards
• Reorganize navigation into Getting Started, User Guide, and Reference sections
• Combine connections.md and redis_modules.md into a single redis_setup.md page
• Recommend Redis 8 as the preferred Redis version

1.0 Code Example Updates

• Add model-level index=True to all indexed model examples
• Update Pydantic validators to v2 syntax (__get_pydantic_core_schema__ instead of __get_validators__)
• Update error message formats to Pydantic v2 style
• Replace deprecated @app.on_event("startup") with lifespan context manager in FastAPI examples
• Replace Migrator().run() references with om migrate CLI

Files Changed

• mkdocs.yml - Theme configuration and navigation
• docs/index.md - Updated landing page and model example
• docs/getting_started.md - Docker images, validators, error messages
• docs/validation.md - Error message formats
• docs/fastapi_integration.md - Lifespan pattern for startup
• docs/migrations.md - Model-level indexing
• docs/redis_setup.md - New combined page (replaces connections.md and redis_modules.md)
• docs/stylesheets/extra.css - Custom styling
• README.md - Updated link to redis_setup.md

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Co-authored by Augment Code