Publish RCs through GitHub Packages

[ShawnChen-Sirius]

Summary

• use the permanent com.clickhouse.chdb Maven coordinates from the first RC
• publish 1.0.0-rc.1 and later RC tags to GitHub Packages
• keep Maven Central publishing for stable releases after Publisher Pro is available
• replace the README script-install example with Maven/GitHub Packages instructions

Validation

• mvn validate
• mvn -pl chdb-jdbc -am test
• workflow YAML parse check

The existing v1.0.0-preview.1 GitHub Release bundle remains separate from the Maven RC flow.

Note

Publish RC artifacts to GitHub Packages via rc-release workflow

• Adds the rc-release GitHub Actions workflow, triggered by RC tag pushes or manual dispatch, which builds JDBC and native artifacts on a four-platform matrix (Linux x86_64/aarch64, macOS x86_64/aarch64) and publishes parent, JDBC, native, and BOM artifacts to GitHub Packages
• Refactors all Maven groupIds from the provisional namespace to the permanent ClickHouse namespace across pom.xml, module POMs, chdb-examples, integration tests, docs, and verify-consumer.sh
• Updates README and publishing docs to describe GitHub Packages PAT and repository configuration, and marks the project status as release candidate
• Risk: the groupId change in every module POM breaks existing dependencies on the old provisional coordinates; consumers must update to the ClickHouse namespace

^{Macroscope summarized 68b66f5.}

[ShawnChen-Sirius]

@wudidapaopao please review this PR