fix: Handle dots in custom field names for segments, workflows, and templates

[chamby]

Summary

• Custom fields with dots in their names (e.g., prefix.key) were silently broken across segment filtering, workflow conditions, and email template rendering because the code split on . to build path lookups, treating them as nested JSON paths instead of literal flat keys
• Fixes SegmentService, WorkflowExecutionService, and template.ts to preserve dots in custom field names
• Backwards-compatible: fields without dots continue to work identically

Fixes #346

Changes

SegmentService.buildJsonFieldCondition — Use [jsonPath] (single-element array) instead of jsonPath.split('.'). Contact data is always a flat JSON object, so the Prisma JSON path should always be a single key.

WorkflowExecutionService.resolveField — Split only on the first . to separate the top-level field name (data) from the custom field name (prefix.key), instead of splitting on every ..

template.ts getValue — Replace split('.').reduce() with a recursive function that tries direct key lookup at each level before descending via dot-splitting. For data.prefix.key, it enters data, then finds prefix.key as a literal key.

Test plan

• Verify dynamic segments match contacts with dotted custom field names (e.g., data.app.plan)
• Verify workflow CONDITION steps correctly evaluate dotted custom fields
• Verify email templates render {{data.prefix.key}} correctly
• Verify existing non-dotted fields (data.plan, data.firstName) continue to work

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