fix: restore generated field create request coverage

[S4Mi]

Summary

• Restores field-create variant generation when source schemas use the current FormBuilder*FieldRequest names instead of legacy unprefixed names.
• Maps regex field creation to the regex request schema and backfills text-validation settings where the generated schema omits them.
• Backfills known form request fields (success_message, error_message, ai_mode, public_stats, public_rows) and answer_description on field request schemas.

Why

The MCP generated artifact had collapsed FormalooFieldCreateRequest to only two branches, so agents lost most field-create schemas and MCP preflight validation became unreliable.

Validation

• ./generate.sh
• Verified MCP artifact has 215 operations and FormalooFieldCreateRequest.oneOf.length === 37 after generation.

Known existing warnings remain for WhatsApp operation descriptions.