docs: improve Examples & Tutorials page with better organization and content
- Reorganize page into clear sections: Getting Started, Ready-to-Deploy, Multi-Agent, Tools & Integrations, SDK Examples, Community Projects, Learning Resources
- Add more examples from Awesome Letta including CharacterAI clone, Deep Research Agent, DuckDB Agent, and various integrations
- Add helpful Info box pointing to Quickstart, DeepLearning.AI Course, and Awesome Letta
- Improve card descriptions to be more informative and action-oriented
- Update title from "Letta Cookbooks" to "Examples & Tutorials" for clarity
- Fix internal tutorial links to use correct /examples/ and /cookbooks/ paths
- Better connect page to rest of documentation and community resources
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