feat: canonical custom field types, validation, and type-aware querying
- Unify field types across all layers: Text, Textarea, SelectOne, SelectMultiple, Date, DateTime, Number
- Add CustomFieldValidationConfig with type-specific Zod schemas
- Add validateCustomFieldValue() dispatching per-type validation
- Add validation_config (JSONB) and default_value columns to custom_fields
- Replace ad-hoc date/datetime/pattern checks with centralized validator
- Type-aware cf.* query operators: gt:, gte:, lt:, lte:, before:, after:, contains:
- Type-aware admin builder UI with inline option editor, min/max, date ranges, constraints
- Type-aware ticket detail rendering: Number inputs, Textarea, SelectMultiple checkbox groups
- Backward compatible: legacy type names mapped to canonical; old pattern field still checked
- Update seed data to canonical PascalCase types
- Migration 0018: add validation_config and default_value to custom_fields
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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