Document JSON Schema compliance status and known limitations

[sergiobayona]

Summary

Create documentation that clearly outlines the current JSON Schema compliance status, known limitations, and roadmap.

Current Status

• 23 of 916 tests passing (2.5% compliance rate)
• Most tests skipped due to architectural constraints, not missing features

Documentation Should Include

1. Architectural Constraints

• EasyTalk models are always objects (can't test primitive root schemas)
• Test data must be Hash (arrays/primitives as root data not supported)

2. Unsupported JSON Schema Features

Document which JSON Schema draft-7 features are not supported:

• not keyword
• anyOf / allOf at root level (property-level oneOf IS supported)
• $ref to remote schemas
• dependencies
• if/then/else
• patternProperties
• propertyNames
• additionalItems
• Boolean schemas

3. Supported Features

Document what IS fully supported:

• Basic type validation (string, integer, number, boolean, array)
• String constraints (minLength, maxLength, pattern, format, enum)
• Numeric constraints (minimum, maximum, exclusiveMin/Max, multipleOf)
• Array constraints (minItems, maxItems, uniqueItems)
• Nested object validation
• T::OneOf, T::AnyOf, T::AllOf for property types
• compose for schema composition

4. Validation Gaps

Document known gaps between JSON Schema validation and ActiveModel validation:

• Empty string handling (presence vs type)
• Error path granularity differences

Files to Create/Modify

• docs/JSON_SCHEMA_COMPLIANCE.md (new)
• Update README.md to reference compliance doc