docs(express): add TypeScript guide for custom session properties (#12590)
* docs(express): add TypeScript guide for custom session properties
docs(express): add TypeScript guide for custom session properties
- Added detailed documentation for extending session types in Express.js
- Included code examples for module augmentation and session callback
- Explained how to add custom properties like `id` to the session object
- Aligned with Auth.js TypeScript best practices and JWT session strategy
This update helps Express.js users integrate custom session properties
with TypeScript support, following the framework's conventions.
* Update docs/pages/getting-started/typescript.mdx
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Co-authored-by: Thang Vu <hi@thvu.dev>