Replace manual GraphQL layer with generated client

[thiagolepidus]

Adds a generated GraphQL client based on the Thoth introspection schema, replacing the previous manually maintained GraphQL model/query/mutation layer.

The generated client exposes typed query, mutation, schema, input, enum and scalar classes, while keeping the dynamic GraphQL\Client API as the main entry point.

Changes

• Adds composer generate-graphql-client to regenerate GraphQL classes from the current schema.
• Generates GraphQL schema objects with getters, setters and toArray() support.
• Generates input classes for mutation arguments, including support for arrays, DTOs with getAllData(), and JsonSerializable values.
• Generates enum/scalar wrappers and PHPDoc for operation methods and schema accessors.
• Adds validation for operation arguments, required inputs, variable types, enum values and selected fields.
• Sends operation arguments as GraphQL variables instead of interpolating values into query strings.
• Preserves GraphQL response error context and wraps transport/schema loading failures with clearer exceptions.
• Removes the old generated Models, QueryProvider, mutation builder and client concern classes.