Add feign-graphql-apt module

[velo]

Summary

• New feign-graphql-apt module: an annotation processor that generates Java types from GraphQL schemas at compile time
• Given a @GraphqlSchema-annotated interface with @GraphqlQuery methods, the processor validates queries against the schema and generates input/result POJOs, enums, and nested types
• Supports deeply nested types, list types, enum generation, transitive type resolution, and deduplication of shared input types

Details

• Annotations: @GraphqlSchema(path) on interface, @GraphqlQuery(query) on methods
• Validation: Queries are validated against the schema with line/column error reporting via Messager
• Type mapping: GraphQL scalars → Java types (Int→Integer, Float→Double, ID→String, etc.), [T]→List<T>, enums → Java enums
• Nested generation: Selection sets produce result types with only selected fields; input types include all schema-defined fields
• Dependencies: graphql-java 22.4, javapoet 1.13.0, auto-service-annotations, compile-testing (test)
• Java 17 required (matches apt-test-generator)

Test plan

• 11 compile-testing tests covering: valid mutation, invalid query error, missing schema error, nested types, enums, list types, shared input deduplication, deeply nested org queries (4+ levels), complex mutation with transitive inputs, search with complex filter inputs, multi-level type reuse
• mvn clean install -pl graphql-apt -Pdev passes

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