Add Jupyter notebook generation, integration tests, and standardize c…

[rlunar]

Add Jupyter notebook generation, integration tests, and standardize cookbook setup

• Add build-notebooks.js to convert markdown cookbooks to .ipynb files (Python → code cells, bash → !-prefixed cells, mermaid → skipped)
• Add dev.js with browser-sync for live reload during development
• Standardize all 51 markdown cookbooks:
  • Docker: use valkey/valkey-bundle:9-alpine everywhere
  • Package installs: pip install → uv pip install + python-dotenv
  • Add load_dotenv() to first import block in each cookbook
  • Add docker setup step to 4 cookbooks that were missing it
  • Update Python version references from 3.9+ to 3.12+
• Add mermaid diagram to semantic-caching getting-started with text fallback, mermaid.js rendering in HTML build
• Add pyproject.toml with base deps + optional groups per framework
• Add pytest integration test suite (53 tests, one per cookbook) that runs cookbook code end-to-end against real Valkey and OpenAI
• Add shared conftest.py with client, raw_client, openai_client, and openai_model fixtures (configurable via env vars)
• Update README with notebook generation instructions