[codex] Add aggregate Maven release validation task

[rz-openai]

Summary

• add a root validateMavenCentralRelease Gradle task
• discover Maven Central publications through the existing snapo.maven.publish convention
• build release AARs, sources, javadocs, module metadata, and POMs for every publication
• build debug variants for Android projects under samples
• reject sample projects that opt into Maven publishing
• emit a deterministic project-path and coordinate manifest for release automation

Why

The release workflow previously invoked the root build task, which built debug and release variants, lint, tests, and packaging for every sample project. The aggregate task makes Snap-O's Gradle model the source of truth for the correct release artifacts and sample validation configurations, without duplicating module lists in release automation.

Impact

New publishable libraries are automatically included after applying snapo.maven.publish. New Android sample projects are automatically validated through assembleDebug.

Validation

• ./gradlew :build-logic:check
• ./gradlew validateMavenCentralRelease --parallel --build-cache
• Java 17 task-graph validation
• generated manifest contains the five expected com.openai.snapo publications
• optimized graph executes 326 tasks versus 755 in the previous root build