[FEATURE] Add GraalVM Native Image compatibility

[DemchaAV]

Goal

Evaluate and add support for using GraphCompose inside GraalVM Native Image applications.

GraphCompose is primarily a library, so compatibility should be verified through a small consumer application rather than by compiling the library itself.

Requirements

• create a minimal native-image smoke-test application;
• depend on graph-compose-core and graph-compose-render-pdf;
• discover the PDF backend through ServiceLoader;
• load fonts and other classpath resources;
• generate a valid PDF from the native executable;
• identify any required GraalVM reachability metadata;
• document supported modules and known limitations;
• add the compatibility test to CI if practical.

Areas to validate

• ServiceLoader backend discovery;
• META-INF/services;
• fonts and bundled resources;
• PDFBox;
• Flexmark;
• optionally evaluate Apache POI-based DOCX and PPTX backends after PDF support is confirmed.

Breaking change

• No — additive compatibility support
• Possibly