feat: add gRPC API Reference example

[devin-ai-integration]

Summary

Adds a new grpc/ example demonstrating how to generate gRPC API Reference documentation from Protocol Buffer (.proto) files. Follows the same structure as the existing graphql/ example with a plant-themed Plant Store gRPC service.

New files:

• grpc/fern/proto/plantstore/v1/plantstore.proto — service with unary and server-streaming RPCs, enums, and messages
• grpc/fern/generators.yml — points to the proto file
• grpc/fern/docs.yml — navigation with Docs + API Reference tabs, flattened: true to reduce sidebar nesting
• grpc/fern/docs/pages/welcome.mdx — landing page
• grpc/fern/docs/pages/api-reference-overview.mdx — overview with card links
• Shared assets and styles (copied from graphql example)

Updated files:

• README.md — added grpc row to examples table
• .github/workflows/check.yml — added grpc to CI matrix
• .github/workflows/preview-docs.yml — added grpc to preview project list
• .github/workflows/publish-docs.yml — added grpc to publish matrix

Review & Testing Checklist for Human

• Verify fern check passes for the grpc example (CI runs this)
• After merge, confirm docs publish to grpc.docs.buildwithfern.com and the API Reference tab renders the proto services/RPCs correctly
• Check that the flattened sidebar navigation looks correct (no deep plantstore.v1 > PlantStoreService nesting)

Notes

• Used remote proto compilation (the default) so no additional tooling (e.g. buf) is needed in CI
• Added flattened: true to the API reference section in docs.yml to reduce sidebar nesting
• The contrast ratio warning for light-mode accent color is pre-existing (same colors as graphql example)

Link to Devin session: https://app.devin.ai/sessions/32ed4c2e39a641468652a38f58330896
Requested by: @devalog

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[github-actions]

🌿 Preview grpc: https://fern-docs-examples-preview-pr13-grpc.docs.buildwithfern.com

Here are the markdown pages you've updated:

• api-reference
• welcome