feat(cli): merge OpenAPI examples with x-fern-examples instead of overriding

[Ryan-Amirthan]

Description

Refs: Requested by @Ryan-Amirthan

When an OpenAPI spec contains both x-fern-examples and standard OpenAPI examples (in requestBody.content.application/json.examples and responses.200.content.application/json.examples), previously only the x-fern-examples were displayed in the API reference. This PR changes the behavior to show both sets of examples.

Link to Devin run: https://app.devin.ai/sessions/a6f0f3945923431fab433900b42bf310

Changes Made

• Added extractOpenAPIExamples() method to extract examples from standard OpenAPI requestBody and responses sections
• Added getRequestBodyExamples() to extract request body examples from application/json content
• Added getResponseBodyExamples() to extract response examples from 200/201/2XX responses
• Modified convertExamples() to merge OpenAPI examples after x-fern-examples (x-fern-examples take precedence by appearing first)
• Request and response examples are matched by index (1st request example pairs with 1st response example)
• Updated test snapshots for examples-endpoint-level, examples-endpoint-level-named, and examples-schema-level fixtures
• Updated test snapshots in packages/cli/register for AI examples and human examples preservation tests
• Added changelog entry (version 3.51.0)
• Updated README.md generator (if applicable)

Human Review Checklist

• Index-based matching: Request/response examples are matched by index. Verify this heuristic is acceptable for cases where the number of request examples differs from response examples
• Snapshot structure changes: The updated snapshots show a simpler example structure (e.g., "treeList" instead of "base_Example list of trees_200"). Some examples now have displayName: undefined, statusCode: undefined, and request: undefined. Verify this is expected and doesn't affect API reference rendering
• Potential data loss: Some snapshots show examples with request: undefined where previously there was request data. Verify this doesn't cause regressions in the API reference display
• Potential duplicates: If x-fern-examples and OpenAPI examples contain similar content, both will now be shown. Consider if deduplication is needed
• Content type limitation: Only application/json examples are extracted. Other content types are not handled

Testing

• Lint checks pass (pnpm run check)
• Test snapshots updated (v3-importer-tests and register package)
• All CI checks passing
• Manual testing with ryanstep-config repo to verify examples appear correctly in API reference

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