docs: add self-hosted SDK setup documentation

[fern-api]

Summary

Adds a Setup section to the self-hosted SDKs page explaining how to use the --local flag with fern generate and configure generators.yml for local SDK generation.

Key additions:

• Instructions for using fern generate --local command
• Configuration examples for outputting SDKs to local file system
• Configuration examples for pushing to GitHub using the GithubSelfhostedSchema (with uri and token properties)

Updates since last revision

• Updated GitHub repository configuration to use the correct GithubSelfhostedSchema which requires uri and token properties instead of repository
• Removed incorrect note about self-hosted Docker image (that image is for docs generation, not SDK generation)
• Rewrote the "How it works" section to remove all Docker image references and accurately describe the CLI-based local generation process
• Corrected process flow order: Organization verification now happens BEFORE SDK generation (not after)
• Added Docker daemon requirement: Added note that Docker daemon must be running on the machine
• Added "Network calls" section: Clarifies that only two network calls are made (org verification and Docker image download) and that no API definition/specification data is sent over the network
• Simplified architecture diagram: Reduced from 5 participants to 3 (Customer, Fern CLI, Fern) for better readability. Docker is now treated as an internal CLI step. Fixed the flow so CLI pushes to output (not Docker directly).
• Added CLI reference documentation: Added --local flag to fern generate command in CLI commands reference with cross-reference to self-hosted page
• Added generators.yml reference documentation: Added new "Self-hosted" accordion to the github section documenting uri and token properties with cross-reference to self-hosted page

Review & Testing Checklist for Human

• Verify process flow order: Confirm that organization verification actually happens before SDK generation when using --local flag
• Verify network call claims: Confirm that only org verification and Docker image download are the network calls, and that no API spec data is sent over the wire (this is a security-relevant claim)
• Verify the GithubSelfhostedSchema properties (uri, token, mode, branch) match the actual schema defined in fern/apis/generators-yml/definition/group.yml
• Confirm Docker daemon requirement is accurate
• Check that cross-reference links work correctly (self-hosted page link from CLI reference and generators.yml reference)

Test plan: Preview the documentation and verify:

1. The Setup section renders correctly with proper code block formatting and tab switching
2. The simplified mermaid diagram renders correctly in the "How it works" section
3. The --local flag appears in the CLI commands reference under fern generate
4. The "Self-hosted" accordion appears in the generators.yml reference under the github section
5. All cross-reference links navigate to the correct pages

Notes

Link to Devin run: https://app.devin.ai/sessions/72c5fdd2a69f470683eb6779d6d21a3f
Requested by: Fern Support ([email protected])

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