feat(cli): add --pr-state option for pull request mode

[devin-ai-integration]

Description

Refs: User request from Niels Swimberghe (@Swimburger)

Adds support for specifying whether generated pull requests should be created as draft or ready for review when using --mode pull-request.

Link to Devin run: https://app.devin.ai/sessions/ced1170e042543a08ede3799b5031869

Changes Made

• Add --pr-state CLI option with choices draft or ready for fern generate command
• Add GithubPullRequestState enum type to Fern definition (group.yml)
• Add pr-state field to GithubSelfhostedSchema and GithubPullRequestSchema in generators.yml configuration
• Pass prState through the generation flow to PR creation logic
• CLI --pr-state takes precedence over generators.yml pr-state config, which defaults to ready
• Add changelog entry for v3.6.0

Usage:

fern generate --group ts-sdk --mode pull-request --pr-state draft

Or in generators.yml:

groups:
  ts-sdk:
    generators:
      - name: fernapi/fern-typescript-sdk
        github:
          uri: org/repo
          token: ${{ GITHUB_TOKEN }}
          mode: pull-request
          pr-state: draft

Human Review Checklist

• The prState parameter is passed to remote generation but not fully utilized there (Fiddle service would need updates) - confirm this partial implementation is acceptable
• PullRequestState type is defined in 3 separate files (generateAPIWorkspaces.ts, runLocalGenerationForWorkspace.ts, runRemoteGenerationForAPIWorkspace.ts) rather than a single source - consider if consolidation is needed
• Verify the auto-generated schema files in packages/cli/configuration/src/generators-yml/schemas/ are correct

Testing

• Unit tests added/updated
• Lint checks pass
• CI checks pass
• Manual testing completed (not performed - would require actual GitHub PR creation)

[devin-ai-integration]

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