Allow creating documents from reference fields

[hfellerhoff]

Summary

• add a small create action to reference-field labels
• open the referenced collection schema in a desktop modal or mobile bottom drawer
• create file-backed and data-document entries, refresh collection data, and select or append the new reference
• derive filenames from completed frontmatter values

Validation

• pnpm check
• pnpm typecheck
• pnpm test
• pnpm build