Add @JsonInclude(NON_NULL) to all generated event classes and warn on…

… Object fallbacks

The code generator (scripts/codegen/java.ts) had two gaps identified
during report-card grading against the Epic #69 rubric:

1. Silent Object fallbacks: When schemaTypeToJava() fell back to
   List<Object> (untyped array) or Map<String, Object> (untyped object
   without properties or additionalProperties), it did so silently.
   Added console.warn() at both sites so type erasure is visible during
   generation, matching the existing warnings for anyOf and unrecognized
   schema patterns.

2. Missing @JsonInclude(NON_NULL) on outer event classes: The annotation
   was present on inner data records and RPC records but missing from
   the SessionEvent sealed base class and all outer event variant
   classes (e.g., AssistantMessageEvent, ToolExecutionStartEvent). Added
   the import and annotation to generateSessionEventBaseClass() and
   generateEventVariantClass().

After regenerating, all 75 session event files and 111 RPC type files
were updated. mvn verify passes with 556 tests, 0 failures, 0 errors.

[maven-release-plugin] copy for tag v0.2.2-java.1

[maven-release-plugin] copy for tag v0.2.2-java.1

[maven-release-plugin] copy for tag v0.2.1-java.1

[maven-release-plugin] copy for tag v0.2.1-java.0

[maven-release-plugin] copy for tag v0.1.32-java.0