Add --deep flag to all fern generate commands in documentation

[fern-support]

Summary

This PR updates all documentation to include the --deep flag when using fern generate commands. The --deep flag enables deep generation mode, which is required for SDK generation with the latest CLI version and ensures that all nested types and dependencies are fully resolved during generation.

Changes

Updated the following documentation files to include --deep flag in all fern generate command examples:

• CLI getting started guide and commands reference
• SDK guides (filtering endpoints, local previews)
• SDK quickstart guides for all supported languages:
  • C# / .NET
  • Go
  • Java
  • PHP
  • Postman
  • Python
  • Ruby
  • Swift
  • TypeScript

Justification

The --deep flag is now a required parameter for SDK generation to ensure proper resolution of nested types and dependencies. This update ensures that all documentation examples reflect the current best practices and prevent users from encountering issues when following the documentation.

All instances of:

• fern generate → fern generate --deep
• fern generate --preview → fern generate --deep --preview
• fern generate --group <name> → fern generate --deep --group <name>

[github-actions]

🌿 Preview your docs: https://fern-preview-2ea449f2-12b0-464a-9df7-242ad11ce460.docs.buildwithfern.com/learn