Add integer type as alias for int32 (JSON Schema compatibility)

[clemensv]

Summary

This PR adds the integer type to the JSON Structure Core specification as an alias for int32.

Changes

• Added integer type definition in the JSON Primitives section (after number)
• The type is defined as an alias for int32 with identical constraints
• Updated the Type System Rules summary to include integer in the JSON Primitives list

Rationale

This addition provides compatibility with JSON Schema, which uses integer as a common type name. Having this alias allows easier migration from JSON Schema to JSON Structure.