feat: add --field option to field add content-relationship and field edit

[angeloashmore]

Resolves: #103

Description

Add a repeatable --field flag to field add content-relationship and field edit for specifying which fields to fetch from related documents.

Fields are validated against the production custom type model via the Custom Types API. Supports dot notation for nested selection through groups and content relationship fields, matching the editor's type builder behavior.

Checklist

• A comprehensive Linear ticket, providing sufficient context and details to facilitate the review of the PR, is linked to the PR.
• If my changes require tests, I added them.
• If my changes affect backward compatibility, it has been discussed.
• If my changes require an update to the CONTRIBUTING.md guide, I updated it.

Preview

How to QA ¹

# Add a content relationship with field selection
prismic field add content-relationship my_cr \
  --to-type blog \
  --custom-type author \
  --field name \
  --field bio

# Edit an existing content relationship to add field selection
prismic field edit my_cr \
  --from-type blog \
  --field name

# Nested selection through groups and CR fields
prismic field add content-relationship my_cr \
  --to-type blog \
  --custom-type author \
  --field name \
  --field social.twitter \
  --field related_author.title

---

Note

Medium Risk
Adds new CLI behavior that fetches and validates remote custom type schemas and mutates the stored customtypes config shape; incorrect resolution/validation could break content relationship configuration. Scope is limited to the field add/edit commands and covered by new tests.

Overview
Adds a repeatable --field option to prismic field add content-relationship and prismic field edit to define which fields are fetched from related documents.

Introduces resolveFieldSelection() in models.ts to validate dot-path selections against the target custom type (including traversal through groups and one nested content relationship) and emit the nested selection structure the Prismic API expects; both commands now fetch the target custom type via the Custom Types API and error if --field is used without exactly one allowed --custom-type.

Adds test coverage for adding/editing a content relationship with field selection.

^{Reviewed by Cursor Bugbot for commit 3f34759. Bugbot is set up for automated code reviews on this repo. Configure here.}

Footnotes

1. Please use these labels when submitting a review:
   ❓ #ask: Ask a question.
   💡 #idea: Suggest an idea.
   ⚠️ #issue: Strongly suggest a change.
   🎉 #nice: Share a compliment. ↩

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

There are 2 total unresolved issues (including 1 from previous review).

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit e3d785e. Configure here.}