fix(cli): support air-gapped environments for protobuf IR generation

[thesandlord]

Description

Refs https://github.com/nominal-io/fern-docs/pull/616

Fixes protobuf IR generation failing in air-gapped/self-hosted environments where buf dep update cannot reach the Buf Schema Registry (buf.build).

Changes Made

• Include buf.lock when copying protobuf files to temp directory (previously explicitly excluded)
• Skip buf dep update network call if a cached buf.lock file already exists
• Added changelog entry for version 3.37.4

This enables self-hosted deployments to work in air-gapped environments by running buf dep update at Docker build time to cache dependencies.

Testing

• Unit tests added/updated
• Manual testing completed (lint/format checks pass)

Human Review Checklist

• Verify the logic: if buf.lock exists → skip network call; if not → run buf dep update
• Consider if there should be a way to force refresh dependencies even when buf.lock exists
• Consider edge cases where cached buf.lock might be stale or incompatible with current deps

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Requested by: @thesandlord
Link to Devin run: https://app.devin.ai/sessions/eadc0db42eec4a538a5f0b4394cc682c

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