Publish ftgo-common and ftgo-common-jpa as shared Maven artifacts

[devin-ai-integration]

Summary

Adds maven-publish plugin configuration so that ftgo-common, ftgo-common-jpa, ftgo-consumer-service-api, and ftgo-restaurant-service-api can be published as standalone Maven artifacts to GitHub Packages. This enables future extracted microservices to depend on these shared modules via standard Maven coordinates (net.chrisrichardson.ftgo:<module>:1.0.0) without needing the monolith source.

Approach: All publishing config is centralized in the root build.gradle using a configure block that targets the four publishable modules by name. No individual module build.gradle files were modified — existing compile project(":ftgo-common") references continue to work unchanged for monolith builds.

Key detail: version = '1.0.0' is set at the project level on publishable modules so that Gradle resolves inter-project dependencies to proper Maven coordinates in generated POMs. Verified locally that ftgo-common-jpa's POM correctly declares net.chrisrichardson.ftgo:ftgo-common:1.0.0 (not unspecified).

Review & Testing Checklist for Human

• Version duplication: version = '1.0.0' appears both as project.version and inside the MavenPublication block. Confirm this is acceptable or consolidate (e.g., use version = project.version inside the publication).
• Setting version on publishable subprojects: This changes project.version from unspecified to 1.0.0 for these 4 modules. Verify no other build logic (e.g., jar naming, other plugins) is affected by this.
• Empty credential fallback: Credentials default to "" if env vars / gradle properties are missing. Consider whether publish should fail fast with a clear error instead.
• End-to-end publish test: Run GITHUB_ACTOR=<user> GITHUB_TOKEN=<pat> ./gradlew :ftgo-common:publish :ftgo-common-jpa:publish against GitHub Packages to verify the full flow. Only publishToMavenLocal was tested in this PR.
• Consume from a separate project: Create a test Gradle project that pulls net.chrisrichardson.ftgo:ftgo-common-jpa:1.0.0 from GitHub Packages (or local Maven) and verify transitive deps resolve correctly.

Notes

• The pre-existing build failure in ftgo-end-to-end-tests-common (missing eventuate-util-test artifact) is unrelated to this change — the eventuate Maven repo was already commented out in the root build.
• No GitHub Actions workflow is included for automated publishing — this is manual-trigger only (./gradlew publish).
• A README.md was added documenting artifact coordinates, consumption instructions, and publish commands.

Link to Devin session: https://app.devin.ai/sessions/315132c28df14cf18922fa23aff8e779
Requested by: @bcmake

[devin-ai-integration]

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